The Role of Protein and Amino Acids in Sustaining and Enhancing Performance (1999) / Chapter Skim
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5 The Energy Costs of Protein Metabolism: Lean and Mean on Uncle Sam's Team
5 The Energy Costs of Protein Metabolism: Lean and Mean on Uncle Sam's Team
Pages 109-120
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From page 109... ...
The traditional credit for coining the word "protein" goes to the Dutch chemist Gerardus Johannes Mulder, who in an article published in the Bulletin des Sciences Physiques et Naturelles en Neerlande on July 30, 1838, stated (in French) that this material was the essential general principle of all of the constituents of the animal body and defined it by the Greek word "proteus," which he translated in Latin to "primaries," that is, the primary constituent of the body (Hartley, 1951~.
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From page 110... ...
These observations are important because one of the principal lessons learned from prior Committee on Military Nutrition Research reports, such as the Ranger studies, is that biological energy demands often far exceed dietary energy intakes in combat field circumstances. Thus, while strength and endurance might immediately be identified with protein metabolism, the energy costs of (1)
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From page 111... ...
(1985) came to roughly similar conclusions but, after addressing Me potential additional costs of all Me cellular regulatory reactions, estimated that these control reactions and over, unaccounted-for, costs would increase the true energy cost of protein metabolism significantly.
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From page 112... ...
Before the cost of protein synthesis itself can be calculated, one must recognize that the proteolytic degradation of cyclins regulates the movement from one phase of the cell cycle to the next through energy-dependent ubiquitin pathways (King et al., 1996; Martin-Castellanos and Moreno, 19971. Of second concern is that mitotic events, including spindle microtubular growth, and spindle elongation during anaphase require hydrolysis of GTP or ATP.
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From page 113... ...
TABLE 5-3 Protein Targeting Costs Nonsecretory Proteins Secretory Proteins Importation of mitochondrial proteins Transit peptide receptor binding- peptide unfolding; Cytosolic competence factor binding & dissociation Matrix/stromal peptidase processing Importation of peroxisomal proteins Importation of nuclear proteins Translocation across the rough endoplasmic reticulum membrane Transport to cis, medial, and bans Golgi Lysosomal and secretory sorting vesicles Acidification of secretary organelles Phosphorylation of receptors/hands Protein folding or"prooLreading" Activation of cytoskeleton motors
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From page 114... ...
What the actual net energy cost of these regulatory events is to the whole body is only speculative, but likely significant. Signal transduction processes, including those mediated by the more than 100 known members of the protein kinase family, and the energy-dependent costs of the second messenger families, for example the phosphatidyl and inositol kineses, are additional energy costs of regulatory protein metabolism.
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From page 115... ...
Rat Models Fasting Metabolic acidosis Renal failure Diabetes mellitus Thermal injury Endotoxin, bacteria Tumors Glucocorticoids Deficient dietary protein Hypothyroidism Increased Protein Degradation Decreased Protein Degradation humans Eating disorders Renal tubular defects Uremia Diabetes mellitus Burns Sepsis Cancer cachexia Cushing's Syndrome Malnutrition Hypothyroidism SOURCE: Adapted from Mitch and Goldberg, 1996
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From page 116... ...
CONCLUSION The energy-dependent processes of maintaining the turnover of body proteins, including synthesis, folding, targeting, regulatory processes, and protein breakdown, have an overall cost to body energy homeostasis that is significantly higher than previously appreciated. The work of Tiao et al.
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From page 117... ...
I guess what I was trying to do was to move us from what I would call the traditional nutritional thinking on this issue, that is, that the costs are related to the net synthesis and oxidation of protein, the protein turnover of macromolecules, and the maintenance of lean mass, and move us to appreciate further that there are additional costs that many physiologists have not spent a lot of time thinking about.
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From page 118... ...
That is, during the period of exercise itself, protein turnover may "turn down, " but there is a period where you have to then "turn it up". I do not think in the context of continued strenuous activity you can significantly reduce the overall cost.
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From page 119... ...
You can look at the contribution of fat and carbohydrate and protein to that negative energy balance. Would you expect anything other than a 4 kcal/g contribution from the protein loss reflecting the savings associated with not supporting some of the synthetic costs?
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