Hormone dependence of the L and M isozymes of pyruvate kinase in isolated rat hepatocytes.

L Pyruvate kinase (LPK) is considered to be the major form in the liver. Two isozymes, LPK and MPK, have been localized in the isolated rat hepatocyte in vitro with an immunocytometric method. MPK is induced by insulin, which also creates a slight stimulation of LPK (at physiological doses) in both fed and fasted animals. Glucagon inhibits LPK in fed animals (the fasting rat is already in a situation of gluconeogenesis and this hormone is ineffective). MPK is insensitive to glucagon, regardless of the nutritional state of the animals. Each PK isozyme is thus controlled predominantly by one of the two hormones, corresponding to a sophisticated regulation of hepatic glycolysis and gluconeogenesis.