SEARCH · PubMed Health

Results for “Efficiency”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 307 records · Page 17Linked to original sources

PubMed1996

Triiodothyronine optimizes sheep ventriculoarterial coupling for work efficiency.

BACKGROUND: Triiodothyronine (T3) administration after cardiopulmonary bypass has been shown to significantly improve cardiac performance. The present study was undertaken to elucidate the effects of T3, when administered as an intravenous bolus, on both cardiac energetics and stroke work-oxygen utilization (EW/LVVO2) efficiency. METHODS: In both unstressed and stressed hearts, energetics were evaluated at baseline and 2 hours after intervention in an in vivo sheep preparation. In the first group (n = 5) sheep received saline vehicle. In the second group (n = 9) sheep received an intravenous bolus of 1.2 micrograms/kg of T3. In the third group (n = 7) sheep received a 2-hour intravenous infusion of dobutamine at a rate of 5 micrograms/kg/min. RESULTS: In the unstressed heart, T3 improved cardiac function at no cost in oxygen consumption by decreasing afterload and hence improved EW/LVVO2 efficiency. In contrast, dobutamine improved unstressed cardiac function by increasing contractility at the cost of increased oxygen consumption and thus decreased EW/LVVO2 efficiency. Triiodothyronine optimized ventriculoarterial coupling for efficiency, but dobutamine optimized coupling for maximal work. In the stressed heart, T3 again improved EW/LVVO2 efficiency, but dobutamine had the opposite effect. CONCLUSIONS: The bolus administration of T3 improves unstressed cardiac performance through optimization of ventriculoarterial coupling for EW/LVVO2 efficiency, primarily through vasodilation. Triiodothyronine also increases efficiency in the stressed heart. This study supports the use of T3 in cardiac operations to improve cardiac performance with no cost in oxygen consumption characteristic of inotropic agents.

Animals↗

PubMed1996

Neck flexor muscle strength, efficiency, and relaxation times in normal subjects and subjects with unilateral neck pain and headache.

OBJECTIVE: To determine the test-retest reliability of a new method for measuring muscular strength, efficiency, and relaxation times of the neck flexor musculature of healthy adults, and to compare these neck flexor muscle properties in subjects who have unilateral neck pain and headache with those in controls. DESIGN: Subjects lay supine and isometrically flexed their necks against a force transducer attached to the back of a webbing and velcro helmet. Electromyograms (EMGs) were recorded from surface electrodes on the sternocleidomastoid (SCM) muscles. Two consecutive sessions of five contractions of varying levels of effort from minimal through moderate and maximal effort were analyzed. SETTING: Ambulatory referral center. PARTICIPANTS: Volunteer control subjects (n = 10, 3 men and 7 women) were recruited from hospital and university personnel. Volunteer neck pain subjects (n = 10, 3 men and 7 women) were recruited from a physiatric chronic pain practice and a hospital outpatient physical therapy practice. RESULTS: In the controls, the intraclass correlation coefficients (ICCs) for the first two maximum neck flexion contractions were; peak force ICC = .81; peak force/body weight ICC = .75; average force ICC = .75; force relaxation time ICC = .73; SCM EMG relaxation times: right ICC = .60 and left ICC = .67. Comparing sessions 1 and 2 the intraclass correlations for SCM efficiencies were right ICC = .58 and left ICC = .97. The peak force in controls (mean = 45.3 +/- 17.6N) was reduced by 50% in the neck pain subjects (mean = 22.4 +/- 13.1N) (p = .004). Similarly, peak force/body weight in the neck pain subjects (X = 0.3 +/- 0.2N/kg) was 46% of control (mean = 0.7 +/- 0.2N/kg) (p = .001), and average force in the neck pain subjects (X = 12.1 +/- 7.5N) was 43% of controls (mean = 28.5 +/- 11.0N) (p = .001). In two neck pain subjects. SCM, EMG and force relaxation times were abnormally long in both the affected and the unaffected SCM muscles, exceeding the control values by greater than 3 standard deviations. The difference between the right SCM efficiency of the control subjects (mean = 0.3 +/- 0.2N/ microV) and the affected SCM efficiency of the neck pain subjects (mean = 0.1 +/- 0.1 N/microV) approached the p < .05 criterion for significance (p = .055). CONCLUSION: The technique was found to be highly reliable for the measurement of neck flexor peak force, peak force/body weight, average force, and force relaxation time, and moderately reliable for the quantitation of SCM EMG relaxation times and SCM efficiency. All force values were significantly lower in the neck pain population compared with the controls. In the neck pain population, force and SCM EMG relaxation times, as well as efficiencies, suggested abnormalities. Neck pain subjects showed no significant differences in SCM EMG relaxation time or SCM efficiency between affected and unaffected SCM muscles.

Adult↗

PubMed2002

Left ventricular oxygen utilization efficiency is impaired in chronic streptozotocin-diabetic sheep.

OBJECTIVE: Energy metabolism is altered in the diabetic heart. However, direct in vivo evidence that diabetes impairs energetics at the chamber level is lacking. Therefore, we investigated the effect of diabetes on left ventricular (LV) energetics in a chronic ovine model. METHODS: Diabetes was induced in Merino-cross sheep with streptozotocin. Experiments were performed in five animals following 12 months untreated diabetes and six animals served as controls. Open-chest anesthetized sheep were instrumented to determine the LV pressure-volume relationship, oxygen consumption and free fatty acid uptake. RESULTS: Diabetes impaired LV contractility (1.5+/-0.5 vs. 2.3+/-0.5 mmHg/ml, P<0.01). Stroke work was preserved but stroke work efficiency (stroke work/pressure-volume area) deteriorated (52+/-4 vs. 58+/-3%, P<0.01). Plasma free fatty acid levels increased (1885+/-1078 vs. 354+/-203 mmol/l, P<0.01) as did LV free fatty acid uptake (312+/-278 vs. 90+/-47 micromol/beat per 100 g LV, P=0.04). Contractile efficiency decreased (31.9+/-1.4 vs. 50.0+/-8.7%, P<0.01) while unloaded oxygen consumption did not change significantly. Therefore, LV oxygen utilization efficiency (stroke work/LV oxygen consumption) was compromised in the diabetic heart (14.9+/-2.8 vs. 24.3+/-4.0%, P<0.001). CONCLUSION: This is the first study to demonstrate that diabetes alters ventricular energetics in vivo. LV oxygen utilization efficiency is impaired as a consequence of decreased contractile efficiency and stroke work efficiency. Impaired efficiency of oxygen utilization may explain in part the increased sensitivity of the diabetic heart to ischemia and the accelerated deterioration of ventricular function in diabetic patients.

Animals↗

PubMed2002

High-efficiency gene transfer to primary T lymphocytes by recombinant adenovirus vectors.

Recombinant, replication-deficient adenoviruses are efficient vectors for gene transfer to a wide range of cell types, with the exception of T lymphocytes. Here, we show that primary T lymphocytes from peripheral blood, cord blood, and the Jurkat T cell line are efficiently transduced by recombinant adenovirus. Nearly 100% infection efficiency of primary T cells is obtained with high multiplicity of infection (MOI) (5000) of recombinant adenovirus coding for lacZ. Similar infection efficiency by adenovirus-mediated gene transfer was obtained at lower MOI (3000) by activating primary T cells with PHA and PMA. Addition of cationic liposomes together with RAdlacZ markedly enhanced the infection efficiency at lower MOI (1000) resulting in over 90% infection efficiency. Primary T cells express low levels of coxsackievirus and adenovirus receptor (CAR), a cell surface receptor for adenovirus fiber attachment, as well as alpha(v)beta(3) and alpha(v)beta(5) integrins, cellular receptors for adenovirus internalization. This suggests that adenovirus entry to T cells at high MOI is mediated by other mechanisms. In conclusion, these results demonstrate that genes can be efficiently transferred to primary lymphocytes by adenovirus vectors at high MOI or in combination with cationic liposomes.

Adenoviridae↗

PubMed2002

Exposure efficiency: an idea whose time has come?

Exposure efficiency, the fraction of material released from a source that is eventually inhaled or ingested, is arguably the simplest of all possible descriptions of the link between pollutant emissions and population exposures. This paper, prepared in late 1999 for the SGOMSEC Workshop, notes that several groups of researchers independently developed the concept of exposure efficiency in the late 1980s and early 1990s but argues that the potential importance of exposure efficiency in risk analysis and life cycle assessment has only recently been appreciated. The paper reviews the history of the concept; discusses and summarizes previous estimates of exposure efficiency for particulate matter and other air pollutants; presents new values for fine particulate matter emitted from power plants and mobile sources in the United States; and illustrates how preliminary estimates of exposure efficiency might be developed. The authors assert that in order for the concept of exposure efficiency to achieve its full potential exposure efficiency estimates for a wide variety of pollutants and sources must be developed and that both the results and methods must be made widely available and accessible to the community of risk assessors and life cycle analysts.

Air Pollutants↗

PubMed1999

Variables affecting the transduction efficiency of adenovirus vectors in bovine aortic endothelial cells.

Features and kinetics of Adenovirus (Ad)-mediated gene transfer to endothelial cells (EC) are not ultimately determined. We tested variables pertinent to the efficiency of Ad-mediated gene transfer to bovine aortic endothelial cells (BAEC) including: (1) Ad-vectors with different promoters, (2) kinetics of transduction efficiency of LacZ gene to BAEC, (3) the concentration and volume of vector-containing medium, (4) the period of incubation time of Ad vectors with BAEC, (5) the duration of transgene expression. An Ad5-LacZ vector with a cytomegalovirus (CMV) promoter transduced the LacZ gene to the cells more efficiently than vectors with the Rous sarcoma virus (RSV) promoter. However, both vectors exhibited a dose-dependent relationship between the vector multiplicity of infection (moi) and the percentage of LacZ-expressing cells. The higher moi of both vectors achieved nearly 100% of transduction efficiency in cultured BAEC. Although the Ad-CMV-LacZ vector better transduced the LacZ gene to BAEC than Ad-RSV-LacZ, a long period of vector exposure to BAEC could overcome the slightly difference in transduction efficiency between the two vectors. These results indicate that both Ad vectors are efficient for gene transfer to endothelial cells, and higher moi of vectors or a longer period exposure of vectors to EC can facilitate efficient transduction of foreign gene into EC in culture.

Adenoviridae↗

PubMed2003

The effect of heating technologies on CO(2) and energy efficiency of Dutch greenhouse firms.

This paper uses Data Envelopment Analysis to compute measures of the efficiency (relative to a frontier) in terms of the use of all inputs as well as for single inputs like CO(2) and energy for a sample of greenhouse firms in the Netherlands over the period 1991-1995. These efficiency measures are generated for different firms specialised in production of vegetables, flowers, and potplants and with different heating technologies. The empirical results indicate that firms use energy quite efficiently and are less efficient in terms of CO(2) emissions. Firms using conventional heating are overall less efficiently using energy and CO(2) than firms using more advanced heating technologies. Most differences in efficiency between firm types and firms using different heating technologies are statistically significant. Scale adjustments can provide an important contribution to further efficiency improvements.

Agriculture↗

PubMedDate not supplied

Fitting methods for constructing energy-dependent efficiency curves and their application to ionization chamber measurements.

An ionization chamber without and with an iron liner (absorber) was calibrated by a set of radionuclide activity standards of the Physikalisch-Technische Bundesanstalt (PTB). The ionization chamber is used as a secondary standard measuring system for activity at the Slovak Institute of Metrology (SMU). Energy-dependent photon-efficiency curves were established for the ionization chamber in defined measurement geometry without and with the liner, and radionuclide efficiencies were calculated. Programmed calculation with an analytical efficiency function and a nonlinear regression algorithm of Microsoft (MS) Excel for fitting was used. Efficiencies from bremsstrahlung of pure beta-particle emitters were calibrated achieving a 10% accuracy level. Such efficiency components are added to obtain the total radionuclide efficiency of photon emitters after beta decay. The method yields differences of experimental and calculated radionuclide efficiencies for most of the photon-emitting radionuclides in the order of a few percent.

Journal Article↗

PubMed2003

Efficiency transfer in the calibration of a coaxial p-type HpGe detector using the Monte Carlo method.

Monte Carlo simulation was applied to the efficiency transfer exercise described in the EUROMET428 project (Appl. Radiat. Isot. 55 (2001) 493), evaluating the peak efficiencies in the energy range 60-2000 keV for a typical coaxial p-type HpGe detector and several types of source configuration: point sources located at various distances from the detector and a cylindrical box containing three matrices. The efficiency values were derived in two ways: (a) by direct calculation taking into account the physical dimensions of the detector provided by the supplier, and (b) by means of relative computation (efficiency transfer) taking also into consideration the known efficiency values for a reference point source. As expected, some significant discrepancies between the calculated and experimental values were found when a direct computation was made using the data provided by the supplier. On the contrary, the results for the peak efficiency derived by relative calculation by means of an efficiency transfer were in good agreement with the experimental values. The deviations found with this last procedure were generally below 5% for all the geometries considered, which is entirely satisfactory for the purposes of routine measurements.

Calibration↗

PubMedDate not supplied

Biodegradable, endosome disruptive, and cationic network-type polymer as a highly efficient and nontoxic gene delivery carrier.

The success of gene therapy is largely dependent on the delivery vector system. Efficient transfection and nontoxicity are two of the most important requirements of an ideal gene delivery vector. To generate both an efficient and nontoxic vector, we rationally constructed polymeric vectors to have simultaneous multiple functions, i.e., controlled degradation, an endosome disruptive function, and positive charges. Remarkably, the transfection efficiency of network poly(amino ester) (n-PAE) synthesized in this manner was comparable to that of polyethylenimine (PEI), one of the most efficient polymeric gene delivery vectors reported to date. However, there was a marked difference in cytotoxicity between the polymers. The majority of PEI-transfected cells were granulated and dead, whereas most of the cells transfected with n-PAE were viable and healthy. Successive events of efficient endosome escape of n-PAE/DNA polyplex and n-PAE biodegradation should result in high transfection efficiency and favorable cell viability response. The n-PAE-mediated transfection was also very efficient in the presence of serum. These data show that the approach we applied is a very appropriate way of making an ideal gene delivery carrier.

Biodegradation, Environmental↗

PubMed1985

Efficiency of in vitro transcription of Dictyostelium discoideum actin gene is affected by the nucleotide sequence of the transcription initiation region.

The actin gene of Dictyostelium discoideum is transcribed faithfully but with very low efficiency in a cell-free system containing HeLa cell extract [Takiya, S., Tabata, T., Iwabuchi, M., Hirose, S., & Suzuki, Y. (1984) J. Biochem. (Tokyo) 95, 1367-1377]. Using the same in vitro system, we determined that the promoter activity of the actin 5 gene is 100-200 times weaker than that of the silkworm fibroin gene. To clarify the cause of the low transcription efficiency, various chimeric genes were constructed from the actin and fibroin genes, and their transcription efficiencies were examined in vitro. Both the TATA box and the transcription initiation site of the two natural genes functioned in the transcription of the chimeric genes, the efficiency of which was especially affected by the transcription initiation region. In chimeric genes having the upstream sequence of the actin gene and a downstream sequence including the transcription initiation site of the fibroin gene, the transcription efficiency was higher than one-third of that of the natural fibroin gene. In chimeric genes having the actin transcription initiation region and an upstream sequence of the fibroin gene, the transcription efficiency was as low as that of the natural actin gene. We concluded that the transcription initiation site is a part of the promoter and an essential region for directing faithful and efficient initiation of gene transcription.

Actins↗

PubMed1989

Terminator-distal sequences determine the in vitro efficiency of the early terminators of bacteriophages T3 and T7.

Bacteriophages T3 and T7 contain homologous terminators for Escherichia coli RNA polymerase that restrict early phage transcription to the leftmost 20% of the linear phage genomes. These two terminators serve equally well as p-independent terminators in vivo, but their in vitro efficiencies and sensitivity to salt and nucleotide concentrations differ dramatically. Sequence analysis shows that the T7 and T3 terminators differ at only two sites in the region normally accepted as defining terminator function. In order to determine which structural features of these two terminators are responsible for their functional differences, a series of hybrid terminators were constructed in which structural features of the two terminators were systematically interchanged. Transcription of hybrid terminator templates revealed that sequences downstream of the termination release sites are responsible for the differences in efficiency of in vitro termination. These sequences also determine the sensitivity of these terminators to elevated salt concentrations and to alterations of substrate concentrations. Alteration of the sequences in the region between three and seven nucleotides downstream of the final T7Te release site is sufficient to reduce termination efficiency to that of T3Te, and point mutations in this region yield terminators with intermediate efficiency. Hence, the determinants of p-independent terminator efficiency in vitro must include elements of the transcription complex other than the structure of the 3' end of the transcript. The termination differences between T7Te, T3Te, and their hybrid derivatives are overcome in vivo; all of these sites become very efficient. This finding further supports the hypothesis that protein factors or other cellular features enhance the efficiency and specificity of p-independent terminators in vivo.

DNA↗

PubMed2006

Single-particle detection efficiencies of aerosol time-of-flight mass spectrometry during the North Atlantic marine boundary layer experiment.

During the North Atlantic marine boundary layer experiment (NAMBLEX) sampling campaign at Mace Head, Ireland, both continental and maritime air masses were sampled. Aerosol was characterized both with a TSI 3800 time-of-flight mass spectrometer (ATOFMS) and a MOUDI microorifice impactor, and particle number counts were measured independently with an aerodynamic particle sizer. The data have been analyzed in order to elucidate factors determining the particle detection efficiencies of the ATOFMS. These are broken down according to the efficiency of the inlet system, the hit efficiency on particles which enter the sensing zone of the instrument and the sensitivity of the measured ion signal to the chemical species. A substantial matrix effect depending on the chemical composition of the aerosol sampled at the time was found, which is reflected in variations in the hit efficiency of particles entering the sensing zone of the instrument with the main desorption-ionization laser. This is in addition to the strong inverse power-law dependence of inlet transmission efficiency on particle diameter. The variation in hit efficiency with particle type is likely attributable to differences in the energetics of laser energy absorption, ablation, and ion formation. However, once variations in both inlet transmission and hit efficiencies are taken into account, no additional matrix dependence of ATOFMS response is required to obtain a linear relationship between the ion signal and the concentration of a particular chemical species. The observations show that a constant mass of material is ionized from each particle, irrespective of size. Consequently the integrated ion signal for a given chemical component and particle size class needs to be increased by a factor related to the cube of particle diameter in order to correlate with the airborne mass of that component.

Aerosols↗

PubMed2005

Effect of OH- on the luminescent efficiency and lifetime of Tb3+-doped yttrium orthophosphate synthesized by solution precipitation.

In this work, we use the solution precipitation method to synthesize Tb3+-doped yttrium orthophosphate, which is a green-emission luminescent material. The evolution of hydrated yttrium orthophosphate (YPO4.2H2O) to dehydrated yttrium orthophosphate (YPO4) is observed in the heat-treatment process, simultaneously, accompanying the structural transformation from monoclinic churchite-type to tetragonal xenotime-type structure. Furthermore, the luminescent efficiency of Tb3+-doped YPO4 presents a sharp jump at a critical temperature in this heat-treatment process. Interestingly, this critical temperature is close to the structural transformation temperature. The remarkable change of luminescent efficiency seems to be related to the structural transformation. However, the FTIR and fluorescent decay measurements at 10 and 300 K indicate that the OH group is the origin of luminescent efficiency change. OH- ions with high vibration frequency provide an efficient means to quench the luminescence. The comparison of the luminescent efficiency, OH- content, and lifetime of 5D4 of Tb3+ between two samples with the same crystal structure proves that the structural transformation has no significant effect on the luminescent efficiency and lifetime. On the basis of these results, it is proposed that correctly preventing OH- ions inside the host matrix or effectively eliminating them may improve the luminescent efficiency greatly. This idea also may be applied to other optical systems.

Journal Article↗

PubMed2003

Strain-dependent differences in the efficiency of transgenic mouse production.

Transgenic mouse production via pronuclear microinjection is a complex process consisting of a number of sequential steps. Many different factors contribute to the effectiveness of each step and thus influence the overall efficiency of transgenic mouse production. The response of egg donor females to superovulation, the fertilization rate, egg survival after injection, ability of manipulated embryos to implant and develop to term, and concentration and purity of the injected DNA all contribute to transgenic production efficiency. We evaluated and compared the efficiency of transgenic mouse production using four different egg donor mouse strains: B6D2/F1 hybrids, Swiss Webster (SW) outbred, and inbred FVB/N and C57BL/6. The data included experiments involving approximately 350 DNA transgene constructs performed by a high capacity core transgenic mouse facility. Significant influences of particular genetic backgrounds on the efficiency of different steps of the production process were found. Except for egg production, FVB/N mice consistently produced the highest efficiency of transgenic mouse production at each step of the process. B6D2/F2 hybrid eggs are also quite efficient, but lyze more frequently than FVB/N eggs after DNA microinjection. SW eggs on the other hand block at the 1-cell stage more often than eggs from the other strains. Finally, using C57BL/6 eggs the main limiting factor is that the fetuses derived from injected eggs do not develop to term as often as the other strains. Based on our studies, the procedure for transgenic mouse production can be modified for each egg donor strain in order to overcome any deficiencies, and thus to increase the overall efficiency of transgenic mouse production.

Animals↗

PubMed1998

Increased muscular efficiency during lactation in Colombian women.

OBJECTIVE: To determine the muscular efficiency of lactating women and compare it to that of nonpregnant, nonlactating (NPNL) women. DESIGN: The study was retrospective. The subjects were selected randomly in the two groups and studied on three occasions (rounds) separated by approximately three months. SUBJECTS: There were 109, 101, and 80 NPNL women and 45, 31 and 16 lactating women in rounds 1, 2 and 3 respectively, 19-43 y of age, living under economically deprived conditions in Cali, Colombia, who participated in the study. METHODS: Muscular efficiency was measured as delta efficiency on a cycle ergometer. RESULTS: Muscular efficiency was significantly higher in lactating women in all three rounds compared to NPNL women. In six women it was possible to measure efficiency at variable times prior to their pregnancies, and again during lactation about three months post partum. There was a statistically significant (P = 0.03) increase in muscular efficiency during lactation. CONCLUSION: Lactation results in about a 5% increase in muscular efficiency which may contribute to the adaptation of the mother to the increased energy demands associated with lactation.

Adult↗

PubMed1994

Constitutive expression of the virulence genes improves the efficiency of plant transformation by Agrobacterium.

Inducible virulence (vir) genes of the Agrobacterium tumefaciens tumor-inducing (Ti) plasmid are under control of a two-component regulatory system. In response to environmental factors (phenolic compounds, sugars, pH) VirA protein phosphorylates VirG, which in turn interacts with the promoters of other vir genes, causing induction. A mutation of virG, virGN54D (which codes for a Asn-54-->Asp amino acid change in the product), causes constitutive expression of other vir genes independent of virA. We have investigated whether providing Agrobacterium with a plasmid containing virGN54D augments the efficiency of transfer of the T-DNA (transferred DNA). For both tobacco and cotton, we observed an enhancement of transformation efficiency when the inciting Agrobacterium strain carries the virGN54D mutation. We also tested whether supplying Agrobacterium with a similar plasmid containing wild-type virG affects the efficiency of T-DNA transfer. An intermediate efficiency was observed when this plasmid was employed. Using a beta-glucuronidase (GUS) reporter gene to assess transient expression of T-DNA after transfer to tobacco and maize tissues, we observed a higher frequency of GUS-expressing foci after inoculation with Agrobacterium strains carrying virGN54D than with Agrobacterium carrying the wild-type virG. Gene-transfer efficiency to maize by an octopine strain was greatly improved upon introduction of virGN54D. Multiple copies of wild-type virG were equally effective in promoting transient expression efficiency in tobacco but were virtually ineffective in maize. We propose the use of virGN54D to improve the efficiency of Agrobacterium-mediated transformation, especially for recalcitrant plant species.

Agrobacterium tumefaciens↗

PubMed1998

Protein folding stability can determine the efficiency of escape from endoplasmic reticulum quality control.

A fraction of each secreted protein is retained and degraded by the endoplasmic reticulum (ER) quality control apparatus that restricts export to correctly folded proteins. The intrinsic biophysical attributes that determine efficiency of escape from this proofreading process have been examined by expressing mutants of bovine pancreatic trypsin inhibitor (BPTI) in yeast. Secretion efficiency is strongly correlated with thermodynamic stability for a series of six point mutations of BPTI. No correlation of secretion efficiency with either oxidative folding or refolding rates in vitro is found; both the rapidly folded Y35L BPTI mutant and the slowly unfolded G36D BPTI mutant exhibit low secretion efficiency. Elimination of cysteines 14 and 38 by mutagenesis does not increase secretion efficiency, indicating that intramolecular thiol/disulfide rearrangements are not primarily responsible for retention and degradation of destabilized BPTI variants. Mutant yeast strains with diminished ER-associated degradation do not secrete BPTI more efficiently, indicating that retention and degradation are separable processes. These data support a model for ER quality control, wherein protein folding is functionally reversible and the relative rates of folding, unfolding, vesicular export, and retention determine secretion efficiency.

Aprotinin↗