Understanding muscle energetics is a problem in optimizing supply of ATP to the demands of ATPases. The complexity of reactions and their fluxes to achieve this balance is greatly reduced by recognizing constraints imposed by the integration of common metabolites at fixed stoichiometry among modular units. ATPase is driven externally. Oxidative phosphorylation and glycogenolysis are the suppliers. We focus on their regulation which involves different controls, but reduces to two principles that enable facile experimental analysis of the supply and demand fluxes. The ratio of concentration of phospho-creatine (PCr) to ATP, not their individual values, sets the range of achievable concentrations of ADP in resting and active muscle (at fixed pH) in different cell types. This principle defines the fraction of available flux of oxidative phosphorylation utilized (at fixed enzyme activities). Then the kinetics of PCr recovery defines the kinetics of oxygen supply and substrate utilization. The second principle is the constancy of PCr and H+ (lactate) production by glycogenolysis due to the coupling of ATPase and glycolysis. This principle enables glycogenolytic flux to be measured from intracellular proton loads. Further simplification occurs because the magnitude of the interacting fluxes and metabolite concentrations are specified within narrow limits when both the resting and active fluxes are quantified. Thus there is a small set of rules for assessing and understanding the thermodynamics and kinetics of muscle energetics.
Conference Article| April 01 2002
Energetics of muscle contraction: the whole is less than the sum of its parts
M. J. Kushmerick;
M. J. Kushmerick 1
*Department of Radiology, University of Washington, Seattle, WA 98195, U.S.A.
†Department of Physiology and Biophysics, University of Washington, Seattle, WA 98195, U.S.A.
‡Department of Bioengineering, University of Washington, Seattle, WA 98195, U.S.A.
1To whom correspondence should be addressed: 1959 Pacific Ave. NE, Box 357115, University of Washington, Seattle, WA 98195-97115, U.S.A. (e-mail firstname.lastname@example.org).
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M. J. Kushmerick, K. E. Conley; Energetics of muscle contraction: the whole is less than the sum of its parts. Biochem Soc Trans 1 April 2002; 30 (2): 227–231. doi: https://doi.org/10.1042/bst0300227
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