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At least 19 recordsLinked to original sources

PubMed1995

[Empty body weight gain, protein, faty and energy deposit and utilization of metabolizable energy for energy deposit in black and white bulls. 2. Relationship between energy deposit and intake of metabolizable energy].

From 6 series of individual feeding experiments with different energy supply (EL = 1.1-1.8; EL = 538 kJ/kg LW0.75) the relationship between the intake of metabolizable energy and live weight gain empty body weight gain and energy deposition was quantified according to a nonlinear regression analysis: intake ME (MJ/d) = A.eB.ED. EBWG. LWG with A = a.LW0.75 B = b.ec.LW The estimated parameters are: [chart: see text] The regression analysis made it possible to estimate the maintenance requirement. Dependent on the variable the following values for maintenance requirements were found: [chart: see text] For the partial utilization of metabolizable energy for energy deposition an average value of 0.37 was obtained by suggestion of a maintenance requirement of 538 kJ/kg LW0.75 and a nonlinear generalization of intake of metabolizable energy. The utilization of metabolizable energy was positively influenced by the metabolizability of the energy of the diet and it was negatively influenced by the energy level. The linear quantification of the relation between the intake of metabolizable energy and the energy deposition led to an utilization of 0.40.

Animals↗

PubMed1994

[Effect of the convertibility of energy (Q) on energy maintenance requirement and utilization and convertible energy for the assessment of ruminants. 2. Energy maintenance requirements and energy utilization].

In growing bulls (290-420 kg LW) and wethers (40-60 kg LW) the energy metabolism was measured by means of indirect calorimetry on 3 steps of energy intake (deposition, maintenance, underfeeding) as a rule with feeding 12 (growing bulls) resp. 8 rations (wethers) with a range of energy metabolizability (q) between 0.74 and 0.47. Investigations were carried out in oxen previously with 9 rations with a range of q between 0.65 and 0.56 were completed by measurements of the energy metabolism with underfeeding and also analysed for the influence of q on energy maintenance requirement and energy utilization. In all 3 animal categories the energy maintenance requirement was not dependent on q significantly. On the nutrition level maintenance the mean energy maintenance requirement amounted to 467 +/- 64 in growing bulls (n = 104), 533 +/- 53 in oxen (n = 44) and 323 +/- 59 kJ ME/kg LW0.75.d in wethers (n = 32). The partial utilization of the metabolizable energy for deposition was influenced significantly (alpha = 0.05) by q in growing bulls only (kpf = -0.1495 + 0.9933q +/- 0.050). A differentiation of the utilization of metabolizable energy for deposition was demonstrable in wethers only with mean values of 50.7% (kf) and of 64.2% (km); km was also independent on q.

Animal Feed↗

PubMed1980

Energy and protein nutrition of early-weaned pigs. 2. Effect of energy intake and energy: protein on energy utilisation and body composition of pigs slaughtered at 32 d.

1. The effect of energy and protein intake on the nitrogen and energy utilization and carcass composition of artificially-reared pigs was studied between 8 and 32 d of age in an experiment employing a 5 x 3 x 2 factorial design. The factors were initially energy:N value (1) (250, 355, 460, 565 or 670 kJ/g N), rate of increase of I (R) at 8 d intervals (0, 12.5 or 25%) and plane of nutrition (three times daily to appetite or 75% of this intake). 2. The range of energy:N values was obtained by formulating five diets based on dried skim milk, lactose and casein and feeding appropriate combinations of two diets. 3. The metabolizable energy (ME) intake, carcass dry matter (DM) content, carcass protein gain and carcass fat gain exhibited significant (P less than 0.001) quadratic responses to I. 4. The carcass fat content in the DM increased from 200 to 342 g/kg ( less than 0.001) and the carcass crude protein (N x 6.25) content decreased from 657 to 519 g/kg with increasing level of I (P less than 0.001). The fat and protein contents were 309 and 556 g/kg and 242 and 610 g/kg respectively on the high and low plane of nutrition (PN) and were significantly different (P less than 0.001). 5. There was a significant I x R interaction in relation to carcass protein gain with the maximum gain occurring at 460 kJ/g N when I was constant and at 355 kJ/g N when R was 25% per 8 d. 6. The proportion of apparent digested N intake retained (N retention (NR):apparent digested N (ADN)) was significantly (P less than 0.001) affected by all three factors and there were significant I x R (P less than 0.001), I x PN (P less than 0.01) and R x R x PN (P less than 0.01) interactions. The maximum value of NR:ADN was 0.80. 7. Carcass fat gain and carcass energy gain exhibited quadratic responses to I reaching maximum values at 460 kJ/g N. The energy content of the live-weight gain increased linearly (P less than 0.001) from 5.79 to 7.90 MJ/kg with increasing level of I. PN and R also produced significant (P less than 0.001) responses the means being respectively 7.52 and 6.39 MJ/kg on the high and low PN and 6.55, 6.94 and 7.38 kJ/kg with increasing value of R. 8. Multiple regression analysis of ME intake on live-weight (W), protein gain (PG) and fat gain (FG) yielded the equation: ME (MJ) = 0.644 W0.75 + 32.6 PG " 48.2 FG. This result is discussed in relation to published values for the energy requirements of the young pig.

Aging↗

PubMed1994

[Effect of the convertibility of energy (Q) on energy maintenance requirement and utilization and convertible energy for the assessment of ruminants. 1. Digestibility of energy and nutrients].

The energy metabolism was measured by means of indirect calorimetry in growing bulls with mean live weights of 290-420 kg and in wethers with mean live weights of 40-60 kg. The animals were fed 12 (bulls) and 8 rations (wethers) with high variation in the nutrients composition and with a range of energy metabolizability (q) between 0.74 and 0.47 on 3 steps of nutrition level (deposition, maintenance, underfeeding) as a rule. The energy digestibility of the 12 rations tested in growing bulls on the nutrition level maintenance was measured between 81.9 and 56.4% and that of the 8 rations tested in wethers was measured between 82.6 and 55.6%. On the high and middle nutrition levels the data of energy and nutrients digestibility in growing bulls and wethers were in good agreement, except the significant lower digestibility of crude protein in cattle. On the low nutrition level digestibility of energy, crude protein, crude cellulose and N free residual substances in wethers was 3-5 digestibility units lower than in bulls. The increase of nutrition level by 1 unit lowered the energy digestibility in bulls by 4.2 and the nutrients digestibility about 4-8%-units (0.7 for starch). In sheep the effect was not so high as in cattle. There were differences in the rumen physiological parameters between the animal species. In the growing bulls' rumen liquid the part of acetate was higher and the parts of propionate and butyrate were lower. The content of NH3 was higher in sheep. The increase of nutrition level caused higher amounts of volatile fatty acids in the two animal species with lowering the part of acetic acid and raising the parts of propionic and butyric acid.

Animal Feed↗

PubMed1993

[Dependence of gross energy, digestive energy and metabolizable energy of feed and the energy disposition on the content of digestible nutrients in relation to starch and sugar. The progress of energetic feed evaluation. 1. Results from studies on swine].

On the basis of an analysis of energy metabolism measurements on adult pigs, fed on 92 ratios with very heterogeneous nutrient composition, the following prediction equations for gross energy (y1), digestible (y2) and metabolizable energy (y3) as well as for energy deposition effect of ratios (y) (kJ) are presented: y1 = 23.6z1 + 39.8z2 + 17.3z3 + 16.0z4 + 18.9z5 y2 = 23.6x1 + 39.8x2 + 17.3x3 + 16.0x4 + 17.2x5 y3 = 20.5x1 + 39.8x2 + 17.3x3 + 16.0x4 + 17.0x5 y = 11.0x1 + 34.0x2 + 12.7x3 + 11.6x4 + 5.0x7 + (12.0-0.14(80-x6))(x5-x7) [table: see text]

Animal Feed↗

PubMed1995

[Empty body weight gain, protein, fat and energy deposit and utilization of metabolizable energy for energy deposit in black and white bulls. 2. Protein, fat and energy deposit].

The protein, fat and energy deposition determined in 6 series of individual feeding experiments with different energy supply on slaughter steps (altogether 458 animals) and whole body analysis were generalized in this publication on nonlinear regression analyses. The protein deposition per kg empty body weight gain is influenced by empty body weight, it takes off with increase of the empty body weight. At low empty body weight (100-200 kg) the protein deposition per kg empty body weight gain is small increased with increasing of empty body weight gain, at high empty body weight it is reduced continuously. The fat deposition per kg empty body weight gain increases progressively with the empty body weight and with the empty body weight gain respectively. The energy deposition per kg empty body weight gain increases with increase of empty body weight and of empty body weight gain. It showed the same development like the fat deposition. The protein, fat and energy deposition per kg live weight gain are calculated and tabulated in dependence on the live weight and the live weight gain.

Animals↗

PubMed2000

Energy requirements derived from total energy expenditure and energy deposition during the first 2 y of life.

BACKGROUND: Current recommendations for energy intake of children are derived from observed intakes. Deriving energy requirements on the basis of energy expenditure and deposition is scientifically more rational than is using the observational approach and is now possible with data on total energy expenditure (TEE), growth, and body composition. OBJECTIVES: The objectives of this study were 1) to define energy requirements during the first 2 y of life on the basis of TEE and energy deposition; 2) to test effects of sex, age, and feeding mode on energy requirements; and 3) to determine physical activity. DESIGN: TEE, sleeping metabolic rate, anthropometry, and body composition were measured in 76 infants. TEE was measured with doubly labeled water, sleeping metabolic rate with respiratory calorimetry, and body composition with a multicomponent model. RESULTS: Total energy requirements were 2.23, 2.59, 2.97, 3. 38, 3.72, and 4.15 MJ/d at 3, 6, 9, 12, 18, and 24 mo, respectively. Energy deposition (in MJ/d) decreased significantly over time (P: = 0.001) and was lower in breast-fed than in formula-fed infants (P: = 0.01). Energy requirements were approximately 80% of current recommendations. Energy requirements differed by age (P: = 0.001), feeding group (P: = 0.03), and sex (P: = 0.03). Adjusted for weight or fat-free mass and fat mass, energy requirements still differed by feeding group but not by age or sex. Temperament and motor development did not affect TEE. CONCLUSION: The TEE and energy-deposition data of these healthy, thriving children provide strong evidence that current recommendations for energy intake in the first 2 y of life should be revised.

Anthropometry↗

PubMed2003

Energy balance and rectal cancer: an evaluation of energy intake, energy expenditure, and body mass index.

Lack of energy balance, or greater energy intake than expenditure as indicated by a large body mass index (BMI), has been associated with colon cancer, although less is known about its association with rectal cancer. In this study, we examined the association between BMI, energy intake, and energy expenditure and their combined effect on rectal cancer risk. A population-based case-control study was conducted in Utah and Northern California. Incident cases (n = 952) of rectal cancer and population-based controls (n = 1205) were interviewed between 1997 and 2002 to obtain detailed information on body size, dietary intake, and physical activity patterns. BMI (kg/m(2)) was not associated with rectal cancer in either men or women. Participation in vigorous leisure-time physical activity over the past 20 yr was associated with a significant 40% reduction in rectal cancer risk. Energy intake was associated significantly with increased risk of rectal cancer, especially among people whose diagnosis was prior to age 60 yr (odds ratio [OR] = 3.9; 95% confidence interval [CI] = 1.7-9.1 for men; OR = 2.8; 95% CI = 1.1-7.2 for women). There was a significant interaction between energy intake and energy expenditure, although not between BMI and either energy intake or energy expenditure. These data suggest that large BMI, an indicator of lack of energy balance, is not an important component of the etiology of rectal cancer. However, both physical activity and energy intake were significantly associated with rectal cancer risk. These data suggest that energy expenditure and energy intake alter rectal cancer risk through mechanisms other than energy balance.

Adult↗

PubMed1982

[Energy maintenance requirement and energy requirement for protein retention in growing rats and broilers. 4. Energy requirement for protein retention in broilers].

The results of measurings of the total metabolism from experiments with 6 male broilers (origin: Tetra B) each, which mainly served the ascertainment of energy maintenance requirement (cf. 2) in the growth range between 100 and 2,000 g with alternating experiment phases on the maintenance and growth level, have also undergone interpretation for the further characterisation of the energy requirement for protein retention. Caused by the sequence of periods chosen, there were compensatory growth effects. Energy retention in % of gross energy varied between the experiments in the limits of 24 and 39%, and concerning energy retention per animal and day there were differences up to 100% between the experiments. The share of protein energy retention in energy retention on average amounted to 38% after a medium-high protein supply and 54% after a high protein supply. The utilisation of metabolisable energy for energy retention was significantly lower from rations of a high protein level (40% crude protein) than from those of a medium-high protein level (20% crude protein). Assuming an energy requirement for fat retention of 1.2 J metabolisable energy per J retention, a requirement of metabolisable energy for 1 J protein retention of 1.68; 1.66 and 1.86 was ascertained in the 3 experiments by means of regression analysis. An energy requirement for maintenance of 423 (30 degrees C), 511 (25 degrees C) and 432 kJ metabolisable energy/kg live weight 0 75 X d (30 degrees C) correlated with these requirement values. Energy requirement for protein retention increased significantly with N-intake and decreased significantly with the daily protein retention rate. There was no dependence on the live weight of the broilers.

Animals↗

PubMed1998

Uncoupling the effects of energy expenditure and energy intake: appetite response to short-term energy deficit induced by meal omission and physical activity.

The effects of two methods of inducing an acute energy deficit (exercise and a low-energy breakfast) on appetite were investigated in 11 healthy females, all of whom were regular exercisers and regular breakfast eaters. There were four experimental days: with exercise and a high-energy (500 kcal) breakfast (EHB), exercise and a low-energy (64 kcal) breakfast (ELB), no exercise and a high-energy breakfast (NEHB) and no exercise and a low-energy breakfast (NELB). Hunger and moods were monitored each hour from 8 a. m. until 5 p.m. Energy and macronutrient intake were measured during an ad libitum lunch test meal 4 h after the exercise and breakfast. Heart rate was continuously monitored using the Polar sport tester. The low-energy breakfasts (ELB and NELB) led to increased hunger during the morning and an increase in energy intake at lunch compared with the high-energy breakfasts. Subjects also experienced significantly more food cravings after LBs than after HBs. Exercise failed to have any significant effect on these variables. Thus, two methods of inducing a short-term energy deficit had markedly different effects on appetite. The low-energy breakfast presumably fails to generate the inhibitory satiety signals induced by the 500 kcal breakfast, whereas the metabolic effects of an exercise session failed to generate excitatory signals to hunger and food intake.

Adult↗

PubMed1987

Energy expenditure, energy balance, and composition of weight gain in low birth weight infants fed diets of different protein and energy content.

The effect of energy and protein intakes on energy expenditure, energy balance, and amount and relative rate of both protein and fat deposition in new tissue was investigated in 19 low birth weight infants whose mean protein and energy intakes, respectively, were 2.24 g/kg/d and 113 kcal/kg/d (formula A, n = 8), 3.6 g/kg/d and 115 kcal/kg/d (formula B, n = 5), and 3.5 g/kg/d and 149 kcal/kg/d (formula C, n = 6). The higher energy intake (formula C) but not the higher protein intake (formula B) resulted in greater energy expenditure. Both the higher protein (formula B vs formula A) and higher energy intakes (formula C vs formula B) resulted in greater weight gain secondary, in group B, to a greater absolute rate of protein deposition and, in group C, to a greater absolute rate of fat deposition. The relative composition of the new tissue deposited reflected the proportional intakes of protein and energy. The numerical value of the protein/fat ratio (g/g) of the new tissue deposited by infants fed formulas A and C, the protein contents of which were low relative to energy contents, were similar and significantly lower than the numerical value of the protein/fat ratio of the new tissue deposited by infants fed formula B, which had a higher protein content relative to energy content. These findings suggest that the composition of weight gain is related to both the absolute amounts and the proportions of dietary protein and energy; thus, both must be considered in formulation of nutritional regimens for LBW infants.

Body Weight↗

PubMed1982

[Energy maintenance requirement and energy requirement for protein retention in growing rats and broilers. 3. Energy requirement for protein retention in rats].

In 4 experiments with 3 X 3 male Wistar rats each, which received rations with different protein content on 3 levels (10-40%), a total of 240 measurings of the total metabolism with the purpose of ascertaining the energy requirement for protein retention were carried out under the conditions of ad libitum feeding in the growth range between approximately 65 and 200 g live weight at a temperature of the environment of 30 degrees C. With 25% crude protein (caseine supplemented with methionine) in the feed mixture, with an energy content of the ration between 18 and 20 kJ/kg dry matter, the N-retention capacity of the animals was largely exhausted. When 150 g live weight were exceeded, the N-retention capacity of the animals decreased considerably. Energy retention in % of gross energy depended on the protein level of the feed rations; in all 4 experiments the rats achieved the highest energy retention with 10% crude protein in the feed. The level of energy utilisation decreased with the increasing protein content of the feed mixture. Requirement values of metabolisable energy per 1 J protein energy retention of 1.69; 1.93; 1.81 and 1.74 J were derived by means of multiple regression analysis for all 4 experiments, assuming the exponent 0.75 for the variable metabolic body size. The application of multiple regression analysis to the values of energy retention measuring in all 4 experiments results in the mean energy requirement of 1.67 J/J protein retention, which completely coincides with previous investigations. When the exponent 0.67 was assumed for the variable metabolic body size, the energy requirement data for the individual experiments resp. after the joint evaluation of all 4 experiments were 1.56; 1.75; 1.68 and 1.56; 1.53 J/J resp. The significant influence of the live weight, the consumption quota of digested nitrogen (protein level of feeding) and the protein retention quota on the value of protein requirement for protein retention was proved. This evidence is discussed with respect to further research for the factorial assessment of the bioenergetic of protein retention.

Animals↗

PubMed1997

Energy balance in a respiration chamber: individual adjustment of energy intake to energy expenditure.

OBJECTIVES: In studies on substrate utilization, a state of energy balance is often required. Energy requirements are based on measured or calculated sleeping metabolic rate (SMR) or basal metabolic rate (BMR). A study was performed to compare this protocol with adjustment of energy intake (EI) to 24 h energy expenditure (24 h EE). DESIGN: In part one, eight subjects spent one night and the subsequent three days in a respiration chamber. On day 1 EI was set at 1.5*SMR. On day 2 and 3 EI was set at 24 h EE of day 1. In part two of the study, an activity protocol was provided while staying in the chamber. 12 subjects spent one night and the subsequent two days in the respiration chamber. On day 1 EI was set at 1.55*SMR and on day 2 EI was set at 24 h EE of day 1. MEASUREMENTS: Sleeping metabolic rate, diet induced thermogenesis, physical activity index and 24 h expenditure were measured using a respiration chamber. SUBJECTS: Eight healthy normal-weight females (age: 22 +/- 3, BMI: 20.9 +/- 1.8) in part one and twelve healthy normal-weight males and females (age: 26 +/- 2, BMI: 21.4 +/- 0.5) in part two of the study. RESULTS: Physical activity index (PAI = 24 h EE/SMR) on day 1 (part 1) was 1.55 +/- 0.04, close to the predicted value of 1.5, but between-subject variation was large (range: 1.39-1.68). Absolute deviation from energy balance reduced significantly from 1.35 +/- 0.30 MJ/d on day 1 to 0.51 +/- 0.21 and 0.31 +/- 0.10 MJ/d on day 2 and 3 respectively (P < 0.05). The latter can be considered as near to energy balance. With the activity protocol (part 2) absolute deviation from energy balance reduced significantly from 0.93 +/- 0.20 MJ/d on day 1 to 0.27 +/- 0.11 MJ/d on day 2 (P < 0.05). CONCLUSION: A three day stay in the chamber allows adjustment of energy intake to energy expenditure, in this way achieving a state close to energy balance. When prescribing an activity protocol the same results can be obtained within two days.

Adaptation, Physiological↗

PubMed1982

[Energy maintenance requirements and energy requirement for protein retention in growing rats and broilers. 1. Energy maintenance requirements of growing rats].

In 4 experiments with 3 times 3 male Wistar rats each, which received rations with different protein contents (10; 25 and 40% crude protein in the dry matter), in the growth range between approximately 65 and 180 g live weight and with an environmental temperature of 30 degrees C, a total of 226 measurings of the total metabolism were carried out on the energy level maintenance, partly also with the insertion of a fasting day. The most important results were: On the energy level maintenance with the simultaneous catabolisation of body fat there was considerable protein energy retention, which amounted to between 30 and 40% of the retention achieved in the growth periods. The energy maintenance requirement can be determined with good reproducibility (standard mean deviation: +/-6%). The average energy requirement directly measured at the feeding level maintenance of 437 kJ metabolizable energy (ME)/kg live weight 0,75.d (n=224) differs insignificantly from the average value obtained by means of multiple regression analysis from experiment periods with feeding for growth 423 kJ ME/kg live weight 0,75.d (n=437). Consequently it is not necessary to differentiate between energy requirement for maintenance and energy requirement connected correlatively with the live weight (metabolic weight of the body) under conditions of growth. Energy maintenance requirement proved to be insignificantly dependent on the amount of protein in the feed. The relative values of protein quotas of 10, 25 and 40% in the feed were 100, 101 and 103%; the expected values (derived from the efficiency of ATP synthesis in the oxidation of carbohydrates and protein) amount of 100, 104 and 109%. The problem of the thermogenous effect of protein, which is also of great importance to human nutrition urgently requires further experimental investigation. For growing rats the best adaptation of the energy maintenance over the investigated period of development is achieved if the 2/3 potence of the live weight is chosen as the expression of the metabolic body weight. With high probability this can also be transferred to the characterisation of protein metabolisation.

Animals↗

PubMed2003

Meals with similar energy densities but rich in protein, fat, carbohydrate, or alcohol have different effects on energy expenditure and substrate metabolism but not on appetite and energy intake.

BACKGROUND: It has been suggested that the satiating power of the 4 macronutrients follows the oxidation hierarchy: alcohol > protein > carbohydrate > fat. However, the experimental evidence for this is still scarce. OBJECTIVE: The goal was to investigate the effects on appetite, energy intake and expenditure, and substrate metabolism of meals rich in 1 of the 4 macronutrients. DESIGN: Subjective appetite sensations, ad libitum food intake, energy expenditure, substrate metabolism, and hormone concentrations were measured for 5 h after breakfast meals with similar energy density and fiber contents but rich in either protein (32% of energy), carbohydrate (65% of energy), fat (65% of energy), or alcohol (23% of energy). Subjects were normal-weight, healthy women (n = 9) and men (n = 10) studied in a crossover design. RESULTS: There were no significant differences in hunger or satiety sensations or in ad libitum energy intake after the 4 meals. Diet-induced thermogenesis was larger after the alcohol meal (by 27%; P < 0.01), whereas protein produced an intermediary response (17%; NS) compared with carbohydrate and fat (meal effect: P < 0.01). After the alcohol meal, fat oxidation and leptin concentrations were greatly suppressed (meal effects, P < 0.0001 and P < 0.05) and triacylglycerol concentrations were as high as after the fat meal. CONCLUSION: Intake of an alcohol-rich meal stimulates energy expenditure but suppresses fat oxidation and leptin more than do isoenergetically dense meals rich in protein, carbohydrate, or fat. Despite differences in substrate metabolism and hormone concentrations, satiety and ad libitum energy intake were not significantly different between meals. Our data, therefore, do not support the proposed relation between the macronutrient oxidation hierarchy and the satiety hierarchy.

Adult↗

PubMed1997

Protein utilization during energy undernutrition in sheep sustained by intragastric infusion: effects of protein infusion level, with or without sub-maintenance amounts of energy from volatile fatty acids, on energy and protein metabolism.

Utilization of endogenous and exogenous energy for protein accretion during energy undernutrition has been studied. Nine lambs nourished by intragastric infusion were given either progressively increasing or decreasing amounts of casein-N up to 2550 mg/kg metabolic weight (W0.75), with or without 250 kJ/kg W0.75 of volatile fatty acids daily. Energy balance (respiration calorimetry) and N balance were measured. While all experimental animals were in negative energy balance, N balance increased curve-linearly with the increase in casein-N infusion and attained positive N balance. Endogenous energy (presumably body fat) was found to meet the energy needs for protein accretion during energy undernutrition. It is concluded that body fat can be effectively utilized to support lean-tissue growth during energy undernutrition, so that the classical nutritional concept of dietary energy:protein ratio is only meaningful when both endogenous and exogenous energy are considered.

Adipose Tissue↗

PubMed1977

Variations in the adenylate energy charge during phased growth (cell cycle) of Candida utilis under energy excess and energy-limiting growth conditions.

The variations in the levels of adenine nucleotides during the phased growth (cell cycle) of the yeast Candida utilis growing under nitrogen, sulfate, or iron limitation with glycerol as carbon source have been determined. Synchronous cultures were obtained by the continuous phasing technique, and the results were compared with those of chemostat cultures growing at similar growth rates and under the same types of nutrient limitation. Whereas the chemostat experiments indicated only the average energy status of cultures growing at random, results from phased cultures showed that the adenylate energy charge, defined as (ATP + (1/2)ADP)/(ATP + ADP + AMP) (where ATP, ADP, and AMP signify adenosine 5'-triphosphate, -diphosphate, and -monophosphate, respectively), varied during the phased growth of the yeast. These variations were related to the stage of development of the cells and to the type of nutrient limitation. In every case the energy charge dropped to a low value during the first half of the phasing cycle (cell cycle). Whereas the energy charge was maintained at relatively high levels (ranging from 0.78 to 0.94), for sulfate- or nitrogen-limited cultures, it was very low when iron was the growth-limiting nutrient (0.44 to 0.78). In spite of the low energy charge, the yeast continued to grow under iron limitation. The main component of the adenylate pool of the iron-limited culture was ADP and not ATP as observed with other types of nutrient limitation. It is concluded that under iron limitation the growth of the organism is limited by energy and that under energy-limited growth the energy charge of a growing organism is maintained at low levels. The reason for maintaining a low energy charge in an energy-limited culture is discussed.

Adenine Nucleotides↗

PubMed1986

An energy 'sources' and 'fractions' approach to the mechanical energy expenditure problem--III. Mechanical energy expenditure reduction during one link motion.

Mechanical energy economy and transformation during one link motion are analyzed on the basis of the theory developed in the previous publications (parts I and II of this series, J. Biomechanics 19, 287-300). The 'compensation coefficient' characterizing mechanical energy economy is introduced. The attempts to estimate MEE using only energy curves and neglecting the powers of real sources of energy implicitly lead to replacement of real force and moment systems by the systems reduced to the centers of mass. But such an unintentional substitution of imaginary sources for real ones, specifically, the reduction of forces acting on the link to the equivalent system, changes estimates of mechanical energy expenditure (MEE). That is why the methods of calculating MEE economy based on the determination of so-called 'quasi-mechanical' work (the sum of the kinetic and potential energy increases per one cycle of motion) are not correct. There are two mechanisms to reduce the MEE using the antiphase fluctuations (corresponding to energy transformations) of the (a) rotational and translational fractions of the total energy (at the expense of the F-sources); (b) potential and kinetic energies (at the expense of the mg-source).

Biomechanical Phenomena↗