Regulatory Properties of Skeletal-Muscle Pyruvate Kinase

Hitherto it has been generally supposed that pyruvate kinase (EC 2.7.1.40) has no significant role in the regulation in vivo of glycolytic flux in skeletal muscle (Carbonell et al., 1973). This supposition, apart from providing an explanation for the apparent lack of potentially regulatory allosteric interactions by skeletal-muscle (M-type) pyruvate kinase, is in agreement with the idea that glycolytic flux in skeletal muscle is regulated primarily, if not exclusively, at the level of phosphofructokinase. However, the concept of the phosphofructokinase-fructose 1,6-bisphosphatase/fructose 6-phosphate-fructose 1,6-bisphosphate substrate cycle (Newsholme, 1976; Katz & Rognstad, 1976) and the postulated pathway of amino acid oxidation and alanine formation in skeletal muscle Goldstein & Newsholme, 1976) suggest that pyruvate kinase in skeletal muscle could indeed have an important regulatory function in viuo. This line of reasoning has led us to re-examine the kinetic properties of pyruvate kinase purified from rabbit skeletal muscle.