Studies with a reconstituted muscle glycolytic system. The rate and extent of creatine phosphorylation by anaerobic glycolysis

Abstract

A mixture of purified muscle glycolytic enzymes was reconstituted and the mixture shown to behave in a fashion analogous to that occurring in vivo. Glycolysis leads to ATP production in muscle and results in the phosphorylation of creatine. The extent of this phosphorylation by anaerobic glycolysis was shown to depend to a small extent on the relative proportions of available P_i and creatine initially, but more importantly on the first step in glycolysis, in this case the enzyme phosphorylase. With less than 0.1% of the phosphorylase in the a form, only about one-third of the creatine was phosphorylated in 30min, whereas with 4% or more of phosphorylase a, 90% of the creatine was phosphorylated within this time. Inclusion of an adenosine triphosphatase decreased the steady-state concentration of phosphocreatine in the system. Calculations of the theoretical concentrations of ADP and AMP showed that phosphorylase b was almost inactive even in the presence of 9μm-AMP, because of ATP inhibition. With phosphorylase a present, glycolysis was able to continue at least until the calculated concentration of MgADP⁻ was only 7μm, and AMP in the sub-μmolar range. The relation of these values to measured concentrations of nucleotides and to phosphorylase a percentages in intact muscle is discussed.