Phosphocreatine creatine

This reaction is strongly exergonic and AG° at 37°C is —42.8 kj/mol. Physiological concentrations of phosphocreatine, creatine, and inorganic phosphate are normally between 1 mMand 10 mM. Assuming 1 mMconcentrations and using Equation (3.12), the AG for the hydrolysis of phosphocreatine is... 

In addition to the processes described above, there still remains one further process which, at least in some cells or tissues, is required prior to the utilisation of ATP in the cytosol that is, the transport of energy within the cytosol, via a shuttle. The transport of ATP out and ADP into the mitochondrion, via the translocase, results in a high ATP/ ADP concentration ratio in the cytosol. However, a high ratio means that the actual concentration of ADP in the cytosol is low, which could result in slow diffusion of ADP from a site of ATP utilisation back to the inner mitochondrial membrane. If sufficiently slow, it could limit the rate of ATP generation. To overcome this, a process exists that transports energy within the cytosol, not by diffusion of ATP and ADP, but by the diffusion of phosphocreatine and creatine, a process known as the phosphocreatine/creatine shuttle. The reactions involved in the shuttle in muscle help to explain the significance of the process. They are ... 

FIGURE 22-26 Biosynthesis of creatine and phosphocreatine. Creatine is made from three amino acids glycine, arginine, and methionine. This pathway shows the versatility of amino acids as precursors of other nitrogenous biomolecules. 

Hochachka, P.W., and M.K.P. Mossey (1998). Does muscle creatine phosphokinase have access to the total pool of phosphocreatine + creatine. Am. J. Physiol. 274 R868-R872. 

The diaphragm is similar to the heart in that it also responds rhythmically to stimulation. After a brief potentiation of muscle twitch, CN (0.1-1 mM) causes a slow progressive depression of contractility of the rat diaphragm. Potentiation is due to an increase in pH from replenishment of ATP by phosphocreatine (creatine kinase mediated transphosphorylation of ADP to ATP). Inhibition of muscle twitch is due to lactate accumulation as well as increased Pj and increased [Mg ] from breakdown of magnesium phosphocreatine. No decreases in ATP or action potential generation were caused by CN treatment in rat diaphragms. Because skeletal muscle,... 

Breccia A, Fini A, Girotti S and Stagni G, Correlation between physico-chemical parameters of phosphocreatine, creatine, and creatinine, and their reactivity with their potential diffusion in tissue, Pharmatherapeutica, 3(4), 227-232 (1982). 

Biosynthesis of phosphocreatine (creatine 5-phosphate) and phosphoarginine (arginine phosphate)... 

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