No abstract

The distribution of pyruvate kinase (ATP pyruvate phosphotransferase, EC 2.7.1.40) in the nervous system has been studied by both immunofluorescence and a histochemical procedure using nitro blue tetrazolium. The localization in various parts of rat central nervous system in situ, cerebellar and cerebral cortex, was compared to that found in vitro in cultures of cerebellum, spinal ganglia, cerebral astrocytes, and skin fibroblasts. (1) Pyruvate kinase was found predominantly in the cytoplasm of neuronal cell bodies. (2) Large neurons were better visualized than small ones. (3) No glial localization was clearly demonstrated in situ, although this does not rule out the presence of some M1 pyruvate kinase. (4) Regions expected to be rich in nerve terminals, such as the cerebellar glomeruli or the cerebellar molecular layer, showed intense staining even when the cell bodies themselves were negative. This was expected, owing to the previous demonstration of the presence of M1 pyruvate kinase in nerve ending by subcellular fractionation methods. (5) The localization was similar in situ and in tissue culture, except that nerve processes were better seen in the latter and astrocytes were sometimes stained in vitro. (6) Variation in intensity of staining was observed in similar cell types in the same section or in the same culture. This could represent different metabolic or functional or maturational states.

No abstract

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.