Seasonal and starvation-induced changes in enzymatic pattern of frog nephron

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Abstract
Oxidative and hydrolytic enzyme activities in the nephron of the frog were investigated using histochemical and spectrophotometric techniques. The distal tubule was found to possess high activities of enzymes of glycolysis and the Krebs cycle, as well as high cytochrome oxidase activity, but had only slight activities of the hexose-monophosphate shunt enzymes. The proximal tubule had high activities of glycolytic enzymes, enzymes of the hexose-monophosphate shunt, and enzymes of the Krebs cycle, except for succinic dehydrogenase, which was present in very low activity. Proximal tubular cytochrome oxidase was found to vary according both to the season and to environ mental conditions. In freshly caught summer frogs it was present in high activity, but in winter frogs or summer frogs starved for periods of 10–30 days, no proximal tubular cytochrome oxidase could be detected, although other proximal tubular enzyme activities remained unchanged as far as could be histochemically determined. The specific activity of cytochrome oxidase in mitochondrial fractions was found to decrease by about 50% in the kidneys of starved and winter frogs, as compared with summer frogs.