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The mode of regulation of pyruvate dehydrogenase ec of lactating rat mammary gland effects of starvation and insulin

, : The mode of regulation of pyruvate dehydrogenase ec of lactating rat mammary gland effects of starvation and insulin. Biochemical Journal 174(2): 553-562

The initial activity of the pyruvate dehydrogenase enzyme [EC] complex in whole tissue or mitochondrial extracts of lactating rat mammary glands was greatly decreased by 24 or 48 h starvation of the rats. Injection of insulin and glucose into starved rats 60 min before removal of the glands abolished this difference in initial activities. The total activity of the enzyme complex in such extracts was revealed by incubation in the presence of free Mg2+ and Ca2+ (more than 10 and 0.1 mM, respectively) and a crude preparation of pig heart pyruvate dehydrogenase phosphatase. Starvation did not alter this total activity. The decline in initial activity of the enzyme complex derived from the glands of starved animals probably was due to increased phosphorylation of its .alpha.-subunit by intrinsic pyruvate dehydrogenase kinase. Starvation increased intrinsic pyruvate dehydrogenase kinase activity in both whole tissue and mitochondrial extracts. Insulin injection into starved animals 30 min before removal of lactating mammary glands abolished the increase in pyruvate dehydrogenase kinase activity in whole-tissue extracts. Pyruvate (1 mM) prevented ATP-induced inactivation of the enzyme complex in mitochondrial extracts from glands of fed animals. In similar extracts from starved animals pyruvate was ineffective. Starvation led to a decline in pyruvate dehydrogenase phosphatase activity in mitochondrial extracts, but not in whole-tissue extracts. These changes in activity of the intrinsic kinase and phosphatase of the pyruvate dehydrogenase complex of lactating rat mammary gland are not explicable by current theories of regulation of the complex.

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