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PubMed2004

Mechanical efficiency during hand-rim wheelchair propulsion: effects of base-line subtraction and power output.

OBJECTIVE: The purpose of this study was to compare four methods of calculating the mechanical efficiency of hand-rim wheelchair propulsion. METHODS: After completing a maximal incremental test, 18 untrained able-bodied males (mean age 22 years) performed four 4-min bouts of exercise (0%, 40%, 55%, and 70% of peak power output) on a wheelchair-ergometer. The mechanical efficiency was calculated during each submaximal bout by the ratio of work accomplished to the amount of energy expended with four indices: gross (no base-line correction), net (resting metabolism as base-line correction), work (unloaded movement as base-line correction) and delta (measurable work as base-line correction) indices. RESULTS: Work efficiency (16.8-13.8%) were significantly higher (P < 0.001) than gross (6.5-8.9%) or net efficiency (9.9-11.1%) at 40-70% peak power output, respectively. Net efficiency was also significantly lower than work efficiency (P < 0.001) at all intensity. Moreover, gross and work efficiency increased and decreases (P < 0.001) respectively with intensity. In contrast, net and delta efficiency remained unchanged. CONCLUSIONS: Depending upon the base-line used, each efficiency index provided different values and were differently affected by the exercise intensity. Precautions should be taken on the conclusions about the mechanical efficiency of hand-rim wheelchair propulsion. Moreover, comparisons between the four efficiency indices among themselves allowed a better and complete description of wheelchair locomotion and wheelchair dependent person. Gross or net efficiencies better reflected the actual mechanical efficiency of the hand-rim wheelchair propulsion whereas work or delta efficiencies investigated the efficiency of muscular contraction during this movement. RELEVANCE: Since the four mechanical efficiency indices measured different aspects of performance, it will have consequences when it comes to choosing an appropriate index. The better understanding of mechanical efficiency index may help future investigators to choose the most appropriate index for their purposes.

Adult↗

PubMed2005

Cross-linked small polyethylenimines: while still nontoxic, deliver DNA efficiently to mammalian cells in vitro and in vivo.

PURPOSE: Polyethylenimine (PEI) is among the most efficient nonviral gene delivery vectors. Its efficiency and cytotoxicity depend on molecular weight, with the 25-kDa PEI being most efficient but cytotoxic. Smaller PEIs are noncytotoxic but less efficient. Enhancement in gene delivery efficiency with minimal cytotoxicity by cross-linking of small PEIs via potentially biodegradable linkages was explored herein. The hypothesis was that cross-linking would raise the polycation's effective molecular weight and hence the transfection efficiency, while biodegradable linkages would undergo the intracellular breakdown after DNA delivery and hence not lead to cytotoxicity. Toward this goal, we carried out cross-linking of branched 2-kDa PEI and its 1:1 (w/w) mixture with a linear 423-Da PEI via ester- and/or amide-bearing linkages; the in vitro and in vivo gene delivery efficiency, as well as toxicity to mammalian cells, of the resultant cross-linked polycations were investigated. METHODS: The efficiency of the cross-linked PEIs in delivering in vitro a plasmid containing beta-galactosidase gene and their cytotoxicity were investigated in monkey kidney cells (COS-7). Dynamic light scattering was used to compare the relative DNA condensation efficiency of the unmodified and cross-linked PEIs. In vivo gene delivery efficiency was evaluated by intratracheal delivery in mice of the complexes of a luciferase-encoding plasmid and the PEIs and estimating the luciferase expression in the lungs. RESULTS: Cross-linking boosted the gene delivery efficiency of the small PEIs by 40- to 550-fold in vitro; the efficiency of the most potent conjugates even exceeded by an order of magnitude that of the branched 25-kDa PEI. Effective condensation of DNA was evident from the fact that the mean diameter of the complexes of the cross-linked PEIs was some 300 nm with a narrow size distribution, while the complexes of the unmodified small PEIs exhibited a mean size of >700 nm with a very broad size distribution. At concentrations where the 25-kDa PEI resulted in >95% cell death, the conjugates afforded nearly full cell viability. The cross-linked PEIs were 17 to 80 times more efficient than the unmodified ones in vivo; furthermore, their efficiencies were up to twice that of the 25-kDa PEI. CONCLUSIONS: Cross-linking of small PEIs with judiciously designed amide- and ester-bearing linkers boosts their gene delivery efficiency both in vitro and in vivo without increasing the cytotoxicity. The high efficiency is dependent on the nature of the linkages and the PEIs used.

Animals↗

PubMed1993

3' RNA processing efficiency plays a primary role in generating termination-competent RNA polymerase II elongation complexes.

In several mammalian transcription units, a transcription termination mechanism in which efficient termination is dependent on the presence of an intact 3' RNA processing site has been identified. The mouse beta maj-globin transcription unit is one such example, in which an intact poly(A) site is required for efficient transcription termination. It is now evident that 3' mRNA processing sites are not always processed with the same efficiency. In this study, we characterized several pre-mRNAs as substrates for the 3' mRNA processing reaction of cleavage and polyadenylation. We then determined whether poly(A) sites which vary in processing efficiency support a poly(A) site-dependent termination event. The level of processing efficiency was determined in vitro by assays measuring the efficiency of the pre-mRNA cleavage event and in vivo by the level of poly(A) site-dependent mRNA and gene product expression generated in transient transfection assays. The beta maj globin pre-mRNA is very efficiently processed. This efficient processing correlates with its function in termination assays using recombinant adenovirus termination vectors in nuclear run-on assays. When the beta maj globin poly(A) site was replaced by the L1 poly(A) site of the adenovirus major late transcription unit (Ad-ml), which is a poor processing substrate, termination efficiency decreased dramatically. When the beta maj globin poly(A) site was replaced by the Ad-ml L3 poly(A) site, which is 10- to 20-fold more efficiently processed than the Ad-ml L1 poly(A) site, termination efficiency remained high. Termination is therefore dependent on the yield of the processing event. We then tested chimeric poly(A) sites containing the L3 core AAUAAA but varied downstream GU-rich elements. The change in downstream GU-rich elements affected processing efficiency in a manner which correlated with termination efficiency. These experiments provide evidence that the efficiency of 3' processing complex formation is directly correlated to the efficiency of RNA polymerase II termination at the 3' end of a mammalian transcription unit.

Adenoviridae↗

PubMed2006

International comparison of the technical efficiency of component preparation.

BACKGROUND: Under economical constraints, blood centers need to identify ways to improve their efficiency. Because there is little evidence regarding the technical efficiency of blood centers, international comparisons may be useful in identifying efficiency discrepancies and can reveal opportunities for enhancing efficiency, such as allocating resources more effectively. STUDY DESIGN AND METHODS: Data were collected for years 2000 through 2002 from 16 blood centers in 10 European countries. Input variables included working hours, whole-blood (WB) collections, premises, and equipment, and the output variables were red blood cells and platelets (PLTs). A nonparametric method, data envelopment analysis (DEA), was used in the analyses of technical efficiency in blood component preparation departments. Efficiency scores were calculated with DEA linear programming techniques and evaluated for site characteristics that possibly affect efficiency, such as the production method of PLTs and the proportion of BCs (buffy coats) from WB and BC PLTs from all PLTs produced. RESULTS: With working hours and equipment as inputs, median technical efficiency was 60 percent (range, 41%-100%). Four departments were efficient (efficiency, > 90%), and 12 were inefficient (range, 41-89). Efficiency remained roughly the same in 13 departments through the 3-year study period and decreased in 3. Efficiency was mainly affected by staffing levels (working hours). Efficiency did not directly relate to production volume, method, or any other site characteristic. CONCLUSIONS: The major cause of inefficiency was excess staffing resulting from a suboptimal combination of manpower and production output levels. Further research is needed to manage factors affecting efficiency, such as the fluctuation of demand in production planning.

Blood Banks↗

PubMed1992

Energy conversion efficiency in human left ventricle.

BACKGROUND: Left ventricular mechanical efficiency is one of the most important measures of left ventricular pump performance. Several clinical studies, however, have shown that mechanical efficiency does not fall substantially as the heart fails. To clarify the insensitivity of mechanical efficiency to the change in pump performance, we analyzed human left ventricular mechanical efficiency, applying the concept of left ventricular systolic pressure-volume area (PVA). METHODS AND RESULTS: PVA correlates linearly with myocardial oxygen consumption per beat (MVO2): MVO2 = a.PVA+b, and represents the total mechanical energy of contraction. We determined MVO2-PVA relation and external work in 11 patients with different contractile states. We also calculated the energy transfer from MVO2 to PVA (PVA/MVO2 efficiency), that from PVA to external work (work efficiency), and mechanical efficiency (external work/MVO2). Left ventricular pressure-volume loops were constructed by plotting the instantaneous left ventricular pressure against the left ventricular volume at baseline and during pressure loading. The contractile properties of the ventricle were defined by the slope of the end-systolic pressure-volume relation (Ees). Pressure elevation raised external work by 41.4%, PVA by 71.2%, and MVO2 by 54.5%. These changes were associated with a decrease in work efficiency and an increase in PVA/MVO2 efficiency. The opposite directional changes in these two efficiencies rendered the mechanical efficiency constant. The slope, a, of the relation between MVO2 and PVA was relatively constant (2.46 +/- 0.33) over the range of 0.8-8.8 mm Hg/ml of Ees, but the oxygen axis intercept, b, tended to decrease with the reduction in Ees. PVA/MVO2 efficiency correlated inversely (r = -0.66, p less than 0.05) with Ees, whereas work efficiency correlated linearly with Ees (r = 0.91, p less than 0.01). CONCLUSIONS: Mechanical efficiency is not appreciably affected by changes in loading and inotropic conditions as long as the left ventricular contractility is not severely depressed.

Cardiac Catheterization↗

PubMed1995

The influence of tendon Youngs modulus, dimensions and instantaneous moment arms on the efficiency of human movement.

The purpose of the study was to examine the influence of passive tendon work on the gross mechanical efficiency of human whole body movement. Seven male subjects participated in the study. They performed repetitive jumps (like skipping) of three different intensities. Metabolic costs and work rates were recorded to obtain mechanical efficiencies. Net joint moments were calculated from film recordings using inverse dynamics. A general stress-strain relationship for tendons was modelled using a quadratic function, including Youngs elastic modulus of tendon tissue and tendon dimensions. Instantaneous tendon moment arms for the largest leg extensor muscles (m. triceps surae and m. quadriceps femoris) were calculated using joint angle-moment arm transfer functions obtained from the literature (cadaver studies) and the tendon work was calculated from the net joint moments. Gross efficiency values of 0.65-0.69 and efficiency values of 0.77-0.80 at the approximate level of the muscle-tendon complexes were observed. The tendons performed 52-60% of the total work. The enhancement of the muscle-tendon efficiency over the maximal theoretical efficiency of the contractile machinery (0.30) could exclusively be explained by the contribution of the tendon work. A clear negative relationship between repetitive jumping with high mechanical efficiency and running economy at 12 km h-1 was found. Using model calculations the gross efficiency and the muscle-tendon efficiency were shown to be sensitive to tendon Youngs modulus, dimensions and moment arms. The efficiencies were most sensitive to changes in the tendon moment arms. A 10% decrease in tendon moment arms resulted in a 13% increase in the gross efficiency. Optimization or minimisation of the mechanical efficiency by changing the tendon variables 5% was followed by changes in mechanical efficiency of +14% and -10%, respectively.

Adult↗

PubMed2001

Longitudinal study of health maintenance organization efficiency.

Longitudinal studies looking at health maintenance organization (HMO) efficiency in the United States have not been performed before this study--previously there have only been small inter-group studies comparing efficiencies. The objectives here were twofold: to analyse HMO efficiency longitudinally, using a data envelopment analysis (DEA) model; and to compare the various types of HMOs and their efficiency using DEA. A cohort of HMOs was followed longitudinally and a number of variables measuring efficiency were studied. Data were derived from the HMO database survey (HCIA Inc.) for 1993-1997. Thirty-six HMOs were followed over a five-year period, and baseline input and output variables were collected. These measures are proxies for efficiency using the DEA methodology. Over all, using the DEA model it was demonstrated that HMOs tended to improve efficiency over time. Independent Practice Association HMOs appeared to show the highest level of improved efficiency. HMO type, profit status, federal eligibility and age were predictive variables for efficiency. Results of this study demonstrate that HMOs are improving efficiency longitudinally, and in general, certain specific models are longitudinally more efficient than others. Moreover, attributes of efficient HMOs have been identified. For policy-makers looking at efficiency, this information can be used to determine which HMO models are more appropriate when trying to achieve cost containment and effectiveness.

Benchmarking↗

PubMedDate not supplied

Cardiac efficiency.

Efficiency is defined as the ratio of the energy delivered by a system to the energy supplied to it. Depending on the particular question being addressed, there exist a plethora of definitions of efficiency in medical texts, thus hampering their comparison. If only the ventricular work seen by the arterial system is under investigation, pressure-volume work will serve as a useful numerator. If, on the other hand, external and internal work together, i.e. the total mechanical work, is of interest, the pressure-volume area might be employed. Total myocardial oxygen consumption (MVO2) will be a useful denominator in the case of aerobic energy production. The MVO2 for the unloaded contraction must be assessed if, as in other energy transfer systems, net efficiency is to be addressed. If even smaller steps in the chain of energy transfer are to be investigated MVO2 for the arrested heart must be assessed. With an appropriate therapy, hemodynamic determinants can be varied, to improve cardiac efficiency. Nonetheless, measurement of all variables necessary for the calculation of efficiency remains a challenge, in particular in the clinical setting. Separation of the direct effects of drugs on efficiency is even more difficult, since hemodynamic conditions can hardly be controlled throughout the observation period, and changes in efficiency might be secondary to changes in hemodynamics. Whether the heart by itself employs mechanisms to improve its efficiency is still a matter of discussion: there is evidence that when oxygen supply decreases, the heart can switch from one substrate to a less costly one, or possibly can improve efficiency through better use of oxygen. Moreover, the heart seems to "sense" an even more decreased oxygen supply and reduce function in response. Myocardial stunning could be regarded as a protective mechanism as well, with function remaining depressed and the oxygen supply being normal or close to normal. One may conclude from the decreased efficiency that the excess oxygen consumption is used up for repair processes. The improved efficiency found in hypertrophied hearts represents another adaptive process. The underlying mechanism is unclear: a shift towards isomyosin V3 or some undefined shift in metabolic pathway is discussed. It is also still a moot question towards which objective the efficiency of the heart is adjusted. It has been described that under physiologic conditions, the efficiency of both the left and the right ventricle ought to be maximized.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1994

Breed effects, dietary energy density effects, and retained heterosis on different measures of gain efficiency in beef cattle.

Retained heterosis for different measures of gain efficiency was estimated in F3 generation castrate male progeny in three composite populations finished on two levels of dietary energy density (2.82 and 3.07 Mcal of ME and 11.50% CP) and serially slaughtered at four end points at intervals of 20 to 22 d. Breed effects were evaluated in nine parental breeds (Red Poll [R], Hereford [H], Angus [A], Limousin [L], Braunvieh [B], Pinzgauer [P], Gelbvieh [G], Simmental [S], and Charolais [C]) that contributed to the three composite populations (MARC I = 1/4 B, 1/4 C, 1/4 L, 1/8 H, 1/8 A; MARC II = 1/4 G, 1/4 S, 1/4 H, 1/4 A; and MARC III = 1/4 R, 1/4 P, 1/4 H, and 1/4 A). Gain efficiency was evaluated in time constant (0 to 207 d), gain constant (310 to 540 kg), carcass weight constant (333 kg), and retail product weight constant (225 and 210 kg) end points and to different marbling score and longissimus muscle fat end points. Expressions of gain efficiency included live weight gain/megacalories of ME and retail product weight/megacalories of ME. Significant differences were observed among breeds in all measures of gain efficiency. Breeds that had the smallest weight to maintain tended to be more efficient in live weight gain in the time constant period, whereas breeds with the highest rate of gain tended to be more efficient in the gain constant period. To marbling score or longissimus muscle fat end points, breeds with the lowest marbling scores and smallest percentage fat in the longissimus muscle on an age constant basis (e.g., Limousin and Gelbvieh) tended to be less efficient, whereas breeds with the highest marbling score and highest percentage of fat in the longissimus muscle on an age constant basis (e.g., Hereford and Angus) tended to be more efficient. Breeds with the highest percentage of retail product (Limousin and Gelbvieh) were more efficient to retail product weight end points, or when retail product weight was the measure of output. Steers fed the higher energy density diet were more efficient in live weight gain to time constant, live weight gain constant, marbling score constant, and longissimus fat constant end points and were more efficient in the production of retail product weight to retail product weight end points because of the shorter period of maintenance. Retained heterosis was not consistent among composites in different measures of gain efficiency. Higher initial weights resulting in greater requirements for maintenance had a negative effect in composites for most measures of gain efficiency.

Adipose Tissue↗

PubMedDate not supplied

[Data envelopment analysis: its use to assess efficiency of hospital preventive medicine services of Andalusia].

BACKGROUND: The evaluation of hospital units efficiency is a major matter of health services management. Among the techniques to measure efficiency. The Data Envelopment Analysis (DEA) can be used in multiple resources units (inputs) obtaining multiple products (outputs). The objective of this study is the evaluation of Hospital Preventive Medicine Services in Andalucia, using the technique DEA. METHODS: The Preventive Medicine Services from seven hospitals of Andalucia were selected. DEA is technique, based on a linear programming, which finds the weights, which make a Service efficient in relation with the rest. The relative efficiency of seven units was calculated. The unit with the best practice was found by means of cross efficiency matrixes. With regard to the inefficient services, their necessity of increasing activities to achieve efficiency was identified. RESULTS: Two efficiency assumptions were elaborated. In the first one, 4 services were efficient (Efficiency = 1) in relation with the rest. In the second one, the Service S.1 was inefficient. Among the efficient units, S.2 shown the highest average efficiency in both assumptions and appeared as the reference unit for all the inefficient ones. CONCLUSIONS: In the evaluation of Preventive Medicine Services efficiency, at least, three of them shown some kind of inefficiency. The Service S.2 was the point of reference for inputs and outputs selected.

Efficiency, Organizational↗

PubMed1985

The relative translation efficiencies of reovirus messenger RNAs.

The relative translation efficiencies of reovirus messenger RNAs were measured by infecting BHK cells with serotype 1, 2, or 3 virus and measuring the rate of formation of each viral protein species and the amount of each viral single-stranded (ss) RNA species present in the infected cells throughout the multiplication cycle. The translation efficiency of each ssRNA species was then calculated as a percentage of the species that was translated most efficiently. The relative translation efficiencies of the various ssRNA species did not change significantly during the multiplication cycle and cognate mRNA species of serotype 1, 2, and 3 virus were generally translated with similar efficiencies. However, the relative translation efficiencies of the individual ssRNA species differed greatly. The most efficiently translated ssRNA species was usually species s4, followed by species m2 which, on average, was translated about two-thirds as efficiently as species s4. Species s2 and s3 were translated slightly less than one-half as efficiently as species s4; species m3, l2, and l3 one-quarter to one-third as efficiently; and species s1 one-twentieth to one-tenth as efficiently. Finally, species l1 and m1 were translated very inefficiently under all conditions; their translation efficiencies were usually no more than 1% of that of species s4.

Animals↗

PubMed2000

Photosynthetic nutrient-use efficiency in three fast-growing tropical trees with differing leaf longevities.

Differences in nutrient-use efficiency have been attributed to differences in leaf habit. It has been suggested that evergreens, with their longer-lived leaves, and therefore longer nutrient retention, are more efficient than deciduous species in their use of nutrients. In tropical trees, however, leaf life span is not always a function of whole-tree deciduousness, leading to the proposal that nutrient-use efficiency is better related to leaf life span than to leaf habit. It was predicted that potential photosynthetic nutrient-use efficiency (maximum potential photosynthesis/leaf nutrient content) would decrease with increasing leaf life span, whereas cumulative photosynthetic nutrient-use efficiency (carbon assimilated over a leaf's life span/total nutrients invested in a leaf) would increase with increasing leaf life span. Potential and cumulative photosynthetic nutrient-use efficiencies (with respect to nitrogen and phosphorus) were measured for three fast-growing tropical trees: Cedrela odorata L. (Meliaceae), Cordia alliodora (R. & P.) Cham. (Boraginaceae), and Hyeronima alchorneoides Allemão (Euphorbiaceae). Mean leaf life spans of the three species varied about threefold and ranged from 50 to 176 days. The predictions were partially supported: Cedrela odorata had the shortest-lived leaves and the highest potential nitrogen-use efficiency, whereas Hyeronima alchorneoides had the longest-lived leaves and the highest cumulative nitrogen- and phosphorus-use efficiencies. Potential phosphorus-use efficiency, however, was invariant among species. It is suggested that there are potential tradeoffs between leaf characteristics that lead to high potential and cumulative nutrient-use efficiencies. High potential nutrient-use efficiency may be beneficial in high-nutrient environments, whereas high cumulative nutrient-use efficiency may be of greater benefit to species in low-nutrient environments.

Costa Rica↗

PubMed2003

[Effects of rhizosphere acidification on phosphorus efficiency in clones of poplar].

Effects of rhizosphere acidification on P efficiency in different poplar clones were conducted by the method of soil culture in greenhouse. Potassium dihydrogen phosphate was applied to furnish 0, 40, 80, and 120 mg P2O5 kg-1. The experiment consisted of three replicates of each treatment, with a pot of 40 kg soil in a randomized block. The results showed that high P efficiency clones, such as S17, S19, and 105, could decrease their pH values in rhizosphere under P deficiency stress much stronger than clones 106, 797, I-69, 1388, and 3,244, which were low P efficiency clones. The most decrement of pH for the former even accounted to 1.32 pH units and the ratios of the decrements were over 10% in comparison with the pH values in bulk soil. Whereas for the latter less than 0.21 pH units and 2.5% of the decreasing ratio respectively. In contrast to low P efficiency clones, high P efficiency clones could acidify their rhizosphere through a kind of specific mechanism because the pH values in rhizosphere of high P efficiency clones were gradually decreased corresponding with the intensity of P deficiency stress and vice versa. The amounts of available P in rhizosphere of clone S17, S19, and 105 reached 2.64, 3.27, and 3.28 mg.kg-1, respectively, obviously higher than those of the other five low P efficiency clones, which all were below 2.00 mg.kg-1 under P deficiency stress, and the summation percentages of available P in rhizosphere were over 60% for all high P efficiency clones, but less than 10% for low P efficiency clones. The amounts of P taken up by high P efficiency clones were statistically greater than by low P efficiency clones. Regression analysis also indicated that the increment of available P in rhizosphere was closely correlated with the decrement of pH values in rhizosphere under P deficiency stress. This demonstrated the impact of rhizosphere acidification on availability of rhizosphere P, and identified that high P efficiency clones could enhance their contents of available P in rhizosphere, absorb more P and thus grow better through rhizosphere acidification depended on deficiency stress.

Hydrogen-Ion Concentration↗

PubMed2006

Relationship between efficiency and pedal rate in cycling: significance of internal power and muscle fiber type composition.

Cycling was performed to test the following two hypotheses: (1) muscular efficiency is unrelated to pedal rate (61, 88, and 115 r.p.m.) for a group of subjects with a wide range of slow twitch (ST) fibers in spite of decreasing whole-body efficiency and (2) muscular efficiency correlates positively with % ST muscle fibers, and this correlation is more pronounced at low pedal rates than at high pedal rates. Whole-body gross efficiency decreased from 20-22% at 61 r.p.m. to 15-18% at 115 r.p.m. Mean muscular efficiency for all subjects (n=16) was approximately 26%, with delta efficiency being constant and muscular efficiency (taking internal power into account) slightly increasing with pedal rate. Muscular efficiency correlated positively (R(2)=0.25) with % ST fibers (21-97% ST in m. vastus lateralis) at 115 r.p.m. while not at 61 and 88 r.p.m. In conclusion, the decrease in whole-body gross efficiency with increasing pedal rate was not explained by a decrease in muscular efficiency, and supported increase in internal power to account for the increase in metabolic power with increasing pedal rate. Furthermore, differences between individuals in muscle fiber type composition affected muscular efficiency, which correlated positively with % ST muscle fibers during fast pedalling.

Adult↗

PubMed1995

The efficiency of translation termination is determined by a synergistic interplay between upstream and downstream sequences in Saccharomyces cerevisiae.

In a recent study we found that the efficiency of translation termination could be decreased several hundred fold by altering the local sequence context surrounding stop codons in the yeast Saccharomyces cerevisiae. Suppression of termination was shown to be mediated by near-cognate tRNA mispairing with the termination codon. We have now examined in greater detail how the local sequence context affects the efficiency of translation termination in this organism. Our results indicate that the sequence immediately upstream of the termination codon plays a significant role in determining the efficiency of translation termination. An extended termination sequence (containing the stop codon and the following three nucleotides) was also found to be a major determinant of termination efficiency, with effects attributable to the fourth nucleotide being largely independent of the termination codon. For the UGA and UAA stop codons, the influence of the fourth position on termination efficiency (from most efficient to least efficient termination) was found to be G > U,A > C, while for the UAG codon it was U,A > C > G. These sequence-specific effects on the efficiency of translation termination suggest that polypeptide chain release factor (or another molecule that may play a role in translation termination, such as rRNA) recognizes an extended termination sequence in yeast. A previous study found a statistically significant bias toward certain tetranucleotide sequences (containing the stop codon and the first distal nucleotide) in several organisms. We found that tetranucleotide sequences most frequently used in yeast are among the most efficient at mediating translation termination, while rare tetranucleotide sequences mediate much less efficient termination. Taken together, our results indicate that upstream and downstream components of an extended sequence context act synergistically to determine the overall efficiency of translation termination in yeast.

Amino Acid Sequence↗

PubMed2004

Biomechanical efficiency is decreased in heart failure during low-level steady state and maximal ramp exercise.

BACKGROUND: Previous studies of biomechanical efficiency (external work/energy input--Watt/O(2) consumed) in heart failure (HF) using cardiopulmonary exercise testing (CPET) and magnetic resonance spectroscopy (MRS) have had discordant results with increased efficiency by CPET and decreased efficiency by MRS. AIMS: Compare biomechanical efficiency of HF subjects and normal controls during steady state (SS=35 W for 6 min) and ramp cycle ergometer exercise. The hypothesis was that HF subjects would have impaired biomechanical efficiency that correlated with HF symptoms. METHODS: Biomechanical efficiency used the actual Vo(2) during exercise and recovery. Gross (Vo(2) above zero), Net (Vo(2) above the resting Vo(2)) and Work (Vo(2) above the unloaded pedaling Vo(2)) efficiencies were calculated. RESULTS: HF subjects had an 18% higher Vo(2) during SS exercise (P=0.029). Biomechanical efficiency was reduced during SS exercise (gross -15%, P=0.019, net -15%, P=0.062, and work -35%, P=0.002). Gross Efficiency during SS exercise had the strongest correlation with HF symptoms (r=0.55). During ramp exercise gross (-26%), net (-10%) and work (-8%) biomechanical efficiency were all reduced (all P<0.05). The slope of the Vo(2)/Watt relationship during ramp exercise had the best correlation with HF symptoms (r=0.46). CONCLUSIONS: HF subjects have an increased O(2) cost/Watt during SS and ramp exercise that correlates with HF symptoms of fatigue and breathlessness. Methods to improve biomechanical efficiency in HF subjects by exercise training or medications may improve the symptoms and the impaired exercise capacity associated with HF.

Blood Pressure↗

PubMed2005

Encapsulation efficiency of water-soluble and insoluble drugs in liposomes prepared by the microencapsulation vesicle method.

The microencapsulation vesicle (MCV) method is a liposome preparation technique that reproducibly produces liposomes with homogeneous particle sizes with a high encapsulation efficiency. Liposomes encapsulating water-soluble drugs, lipophilic drugs and an amphiphilic drug were prepared by the MCV method and the encapsulation efficiency of the drugs was examined. Three kinds of egg yolk lecithin with different iodine values, i.e., purified egg yolk lecithin (PEL), partially hydrogenated purified egg yolk lecithin (R-20) and completely hydrogenated purified egg yolk lecithin (R-5), were used for membrane materials in order to explore the possible effects of membrane rigidity or surface area on the encapsulation efficiency of the drug. Water-soluble 5-fluorouracil showed 12-15% encapsulation efficiency, which was higher than those reported in the literature (less than 10%). With the MCV method, theoretically the initial drug-containing water phase was always separated from the dispersion medium by the lecithin-containing oil phase, which was advantageous to maintaining a higher encapsulation efficiency of the water-soluble drug. The encapsulation efficiency of lipophilic ibuprofen and flurbiprofen was around 90%. As for ketoprofen and liposomes were not formed when using hydrogenated egg yolk lecithin R-5, while the encapsulation efficiency using PEL or R-20 was around 80%. Amphiphilic amitriptyline hydrochloride resulted in a slightly higher encapsulation efficiency when dissolved in the water than the chloroform. Among the three kinds of lecithin, the most unsaturated PEL tended to show a higher encapsulation efficiency, probably due to differences in the packing geometry of the hydrophobic carbon chains in the membrane bilayer. The encapsulation efficiency of these drugs strongly correlated to the logP(octanol/water) and also tended to correlate to the logP(chloroform/water) for the order of the logP(chloroform/water) was almost the same as the order of the logP(octanol/water) in the drugs examined. As far as the results of this study, the logP(octanol/water) was considered to be a better indicator of the encapsulation efficiency of a drug in the MCV method.

Chemistry, Pharmaceutical↗

PubMed1999

Lectin enhancement of the lipofection efficiency in human lung carcinoma cells.

Poor transfection efficiency of human lung carcinoma cells by lipofection begs further development of more efficient gene delivery strategies. The purpose of this study was to determine whether lectins can improve the lipofection efficiency in lung carcinoma cells. A549, Calu3, and H292 cells grown to 90% confluence were transfected for 18 h with a plasmid DNA containing a beta-galactosidase reporter gene (pCMVlacZ) using lipofectin plus a lectin as the vector. Ten different lectins, which exhibit a wide range of carbohydrate-binding specificities, were examined for their abilities to enhance the efficiency of lipofection. The transfected cells were assessed for transfection efficiency by beta-galactosidase activity (units/microg protein) and % blue cells following X-Gal stain. Lipofectin supplemented with Griffonia simplicifolia-I (GS-I) yields largest enhancement of the lipofection efficiency in A549 and Calu3 cells (5.3- and 28-fold, respectively). Maackia amurensis gives the largest enhancement (6.5-fold) of lipofection efficiency in H292 cells. The transfection efficiency correlates with the amounts of DNA delivered to the nucleus. Binding of FITC-labeled GS-I and the enhancement of the lipofection efficiency by GS-I were inhibited by alpha-methyl-D-galactopyranoside, indicating an alpha-galactoside-mediated gene transfer to lung carcinoma cells. We conclude that lectin-facilitated lipofection is an efficient gene delivery strategy. Employment of cell type-specific lectins may allow for efficient cell type-specific gene targeting.

Humans↗