Protein Turnover With Special Reference to Man

Waterlow, J. C.

doi:10.1113/expphysiol.1984.sp002829

Cited by 282 publications

(147 citation statements)

References 75 publications

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“…However, due to the development of the digestive tract and the high ingestion of forages, relative contributions are 16% and 29%, 17% and 31%, 18% and 20% for PVD, liver and muscles, respectively, in weaned, growing and adult ruminants (for review, see Ortigues and Doreau, 1995;Bauchart et al, 1996;Chilliard et al, 1998). Similar findings have been reported with regard to the contribution of different tissues to whole-body protein synthesis, with for example relative contributions of 18%, 24% and 25% for intestine, liver and muscles, respectively, in the rat (Waterlow, 1984). Consequently, the metabolic fate of nutrients in the splanchnic tissues is of prime importance to control nutrient supply and use in peripheral tissues.…”

Section: Effect Of Nutrition Levelsupporting

confidence: 55%

Responses to nutrients in farm animals: implications for production and quality

Hocquette

Tesseraud

Cassar-Malek

et al. 2007

Animal

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It is well known that any quantitative (energy and protein levels) and qualitative (nature of the diet, nutrient dynamic) changes in the feeding of animals affect metabolism. Energy expenditure and feed efficiency at the whole-body level, nutrient partitioning between and within tissues and organs and, ultimately, tissue and organ characteristics are the major regulated traits with consequences on the quality of the meat and milk produced. Recent progress in biology has brought to light important biological mechanisms which explain these observations: for instance, regulation by the nutrients of gene expression or of key metabolic enzyme activity, interaction and sometimes cross-regulation or competition between nutrients to provide free energy (ATP) to living cells, indirect action of nutrients through a complex hormonal action, and, particularly in herbivores, interactions between trans-fatty acids produced in the rumen and tissue metabolism. One of the main targets of this nutritional regulation is a modification of tissue insulin sensitivity and hence of insulin action. In addition, the nutritional control of mitochondrial activity (and hence of nutrient catabolism) is another major mechanism by which nutrients may affect body composition and tissue characteristics. These regulations are of great importance in the most metabolically active tissues (the digestive tract and the liver) and may have undesirable (i.e. diabetes and obesity in humans) or desirable consequences (such as the production of fatty liver by ducks and geese, and the production of fatty and hence tasty meat or milk with an adapted fatty acid profile).

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Section: Effect Of Nutrition Levelsupporting

confidence: 55%

Responses to nutrients in farm animals: implications for production and quality

Hocquette

Tesseraud

Cassar-Malek

et al. 2007

Animal

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“…Protein synthesis accounts for 18-20 % of whole body ATP use in mammals (Waterlow, 1984) (Pall, 1985). Heart, skeletal muscle and parts of brain and kidney contain an ATP-inhibitable K+ channel which controls plasma membrane potential (reviewed in Ashcroft, 1988).…”

Section: Application Of Metabolic Control Theorymentioning

confidence: 99%

Control of respiration and ATP synthesis in mammalian mitochondria and cells

Brown

1992

Biochemical Journal

563

308

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We have seen that there is no simple answer to the question ‘what controls respiration?’ The answer varies with (a) the size of the system examined (mitochondria, cell or organ), (b) the conditions (rate of ATP use, level of hormonal stimulation), and (c) the particular organ examined. Of the various theories of control of respiration outlined in the introduction the ideas of Chance & Williams (1955, 1956) give the basic mechanism of how respiration is regulated. Increased ATP usage can cause increased respiration and ATP synthesis by mass action in all the main tissues. Superimposed on this basic mechanism is calcium control of matrix dehydrogenases (at least in heart and liver), and possibly also of the respiratory chain (at least in liver) and ATP synthase (at least in heart). In many tissues calcium also stimulates ATP usage directly; thus calcium may stimulate energy metabolism at (at least) four possible sites, the importance of each regulation varying with tissue. Regulation of multiple sites may occur (from a teleological point of view) because: (a) energy metabolism is branched and thus proportionate regulation of branches is required in order to maintain constant fluxes to branches (e.g. to proton leak or different ATP uses); and/or (b) control over fluxes is shared by a number of reactions, so that large increases in flux requires stimulation at multiple sites because each site has relatively little control. Control may be distributed throughout energy metabolism, possibly due to the necessity of minimizing cell protein levels (see Brown, 1991). The idea that energy metabolism is regulated by energy charge (as proposed by Atkinson, 1968, 1977) is misleading in mammals. Neither mitochondrial ATP synthesis nor cellular ATP usage is a unique function of energy charge as AMP is not a significant regulator (see for example Erecinska et al., 1977). The near-equilibrium hypothesis of Klingenberg (1961) and Erecinska & Wilson (1982) is partially correct in that oxidative phosphorylation is often close to equilibrium (apart from cytochrome oxidase) and as a consequence respiration and ATP synthesis are mainly regulated by (a) the phosphorylation potential, and (b) the NADH/NAD+ ratio. However, oxidative phosphorylation is not always close to equilibrium, at least in isolated mitochondria, and relative proximity to equilibrium does not prevent the respiratory chain, the proton leak, the ATP synthase and ANC having significant control over the fluxes. Thus in some conditions respiration rate correlates better with [ADP] than with phosphorylation potential, and may be relatively insensitive to mitochondrial NADH/NAD+ ratio.(ABSTRACT TRUNCATED AT 400 WORDS)

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“…It is usual to suggest that protein metabolism accounts for a large fraction of total body metabolism. In skeletal muscle, protein turnover reportedly accounts for about 20% of the resting metabolism [9, 188,189], but there are large differences between the various organs, and the turnover rate is expected to show species dependency, i.e., to be highest in small animals [8]. One of us [2] made a calculation for rat cardiac muscle based on a protein turnover of 15% per day, a protein content of 15% wet weight, and a caloric equivalent of 5.9 kJ/g protein [190], which suggested an energy usage of approximately 1.5 mW g Ϫ1 .…”

Section: Contributors To the Energymentioning

confidence: 99%

Cardiac Basal Metabolism.

Gibbs

Loiselle²

2001

JJP

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The cardiac basal metabolism is the rate of energy expenditure of the quiescent myocardium. It is also called the resting metabolism or the arrested heart metabolism. It has been measured in numerous ways, and in vivo there is good evidence that it accounts for about 1/5 to 1/3 of the total energy flux. The difficulty arises, however, when the heart is stopped because the magnitude of the basal metabolism depends, as blood viscosity, on how and under what physiological condition it is measured. It is possible for the in vivo basal value to fall to less than 1/5 of its original value without cellular damage or to increase to values 5 times greater than its probable in vivo magnitude (i.e., to rise to values in excess of the energy flux of the normally beating heart) by altering the composition of the perfusion medium. We have written on this subject several times [1][2][3], but believe that developments in knowledge now make it possible for us to speculate in a more informed manner. Since several million openheart operations are performed on arrested hearts worldwide each year, it would seem imperative that we understand the cellular mechanisms that can change the magnitude of basal metabolism.A. V. Hill [4] has pointed out that in examining physiological activities, it is necessary to assume a baseline from which some quantity or rate can be measured. If the energy flux produced by the beating heart were very large compared with the energy flux of the arrested heart, baseline ambiguity would be relatively unimportant. But this is not so in regard to the heart; its basal metabolism is high. Within a species, the basal metabolism of cardiac tissue is several-fold higher than the resting metabolism of skeletal muscle and is an order of magnitude greater than the resting metabolism of amphibian skeletal muscle.Species differences are clearly evident in the magnitude of cardiac basal metabolism, and we believe that the major reason for these differences relates to the leakiness of cell membranes, such as those of the sarcolemma and sarcoplasmic reticulum and those of Japanese Journal of Physiology, 51, 399-426, 2001 Key words: whole hearts, isolated preparations, biochemical contributors, modifiers, species difference, temperature, substrate, hypoxia. Abstract:We endeavor to show that the metabolism of the nonbeating heart can vary over an extreme range: from values approximating those measured in the beating heart to values of only a small fraction of normal-perhaps mimicking the situation of nonflow arrest during cardiac bypass surgery. We discuss some of the technical issues that make it difficult to establish the magnitude of basal metabolism in vivo. We consider some of the likely contributors to its magnitude and point out that the biochemical reasons for a sizable fraction of the heart's basal ATP usage remain unresolved. We consider many of the physiological factors that can alter the basal metabolic rate, stressing the importance of substrate supply. We point out that the protective effect of hypothermia ...

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Protein Turnover With Special Reference to Man

Cited by 282 publications

References 75 publications

Responses to nutrients in farm animals: implications for production and quality

Responses to nutrients in farm animals: implications for production and quality

Control of respiration and ATP synthesis in mammalian mitochondria and cells

Cardiac Basal Metabolism.

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