Journal ArticleDOI
A simple analysis of the "phosphocreatine shuttle"
TLDR
Experimental results demonstrating the transport aspects of the CK reaction emphasize only one feature of a more general notion of facilitated diffusion by near-equilibrium metabolic reactions and do not per se establish the existence of any physical or functional compartmentation of ATP, ADP, PCr, or creatine.Abstract:
The diffusive mobility of solutes chemically connected by reversible reactions in cells is analyzed as a problem of facilitated diffusion. By this term we mean that the diffusive flux of any substance, X, which is in one metabolic pathway, is effectively increased when it participates in a second and equilibrium reaction with another substance Y because the total flux of X in the pathway is the sum of the fluxes of X and Y. This notion is generalized and is seen to include the familiar enhanced intracellular diffusion of oxygen by oxymyoglobin. In this framework the function of creatine kinase (CK) is seen to have two aspects: 1) phosphocreatine (PCr) via the CK reaction buffers the cellular ATP and ADP concentrations and 2) transport of high-energy phosphates is predominantly in the chemical form of PCr. This predominance of PCr is a consequence of the maintained ATP, ADP, and total creatine levels and of the apparent equilibrium constant of the reaction. Thus experimental results demonstrating the transport aspects of the CK reaction emphasize only one feature of a more general notion of facilitated diffusion by near-equilibrium metabolic reactions and do not per se establish the existence of any physical or functional compartmentation of ATP, ADP, PCr, or creatine. PCr can be a large source for increasing inorganic phosphate levels during contractile activity, possibly as a metabolic regulator. Neither the transport nor buffer aspects can be quantitatively important in cells with small distances between ATP-utilizing and ATP-generating sites, such as is the case with cardiac myofibrils and mitochondria.read more
Citations
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Russell S. Richardson,S. C. Newcomer,Tomas A. Schiffer,Björn Ekblom,Jon Lundberg,Eddie Weitzberg,Filip J. Larsen,Javier González-Gallego,Paula Rodriguez-Miguelez,Elena Lima-Cabello,Susana Martínez-Flórez,Mar Almar,J María +12 more
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Impact of Hypohydration and Creatine Supplementation on Skeletal Muscle Performance and Metabolism.
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Energy metabolism patterns in mammalian myocardium adapted to chronic physiopathological conditions
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Effect of citrulline malate supplementation on muscle function and bioenergetics during short-term repeated bouts of fatiguing exercise
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Transport of energy in muscle: the phosphorylcreatine shuttle
Samuel P. Bessman,Paul J. Geiger +1 more
TL;DR: It was proposed in 1951 that contracting muscle fibers liberate creatine, which acts to produce an acceptor effect--later called respiratory control--on the muscle mitochondria, which established a molecular basis for a phosphorylcreatine-creatine shuttle for energy transport in heart and skeletal muscle.
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TL;DR: The observed equilibrium constants (Kobs) of the creatine kinase, myokinase, glucose-6-phosphatase, and fructose-1,6-diph phosphatase reactions have been determined at 38 degrees C, pH 7.0, ionic strength 0.25, and varying free magnesium concentrations.
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