The control of citric acid enzymes in acinetobacter.

2015-11-19T09:08:42Z (GMT) by Helena. Jaskowska-Hodges
The activities of Acinetobacter lwoffi pyruvate dehydrogenase and succinate thiokinase have been shown to be under adenylate control. Pyruvate dehydrogenase was stimulated by AMP and ADP whereas ATP was inhibitory. The products NADH and acetyl-CoA inhibited the enzyme and AMP decreased the latter inhibition. On the other hand, A. Iwoffi succinate thiokinase utilised ADP (Km = l.l8mM), or GDP ( Km = 0.026mM), or IDP (Km = 0.023mM) as nucleotide substrate, and the GDP- or IDP- dependent activities were inhibited by ATP in the presence of nucleoside diphosphate kinase. Thus adenylate control of this enzyme may either be a consequence of the sensitive operation of the enzyme over the range in which the intracellular ADP concentrations may vary, or it may involve a nucleoside diphosphate kinase mediated interaction of ATP with the GDP or IDP pools. No adenylate control was observed with A. lwoffi aconitase, succinate dehydrogenase, fumarase and malate dehydrogenase. Therefore, these results together with those previously observed with citrate synthase, isocitrate dehydrogenase and ?-oxoglutarate dehydrogenase suggest that adenylate control of the citric acid cycle enzymes in A. lwoffi is exerted only on those enzymes which occur at the metabolic branch-points. This novel form of regulation in which several enzymes of a metabolic sequence are controlled by the same effector has been called "multipoint" control and presumably ensures that cycle activity 'is not limited by the withdrawal of intermediates. An examination of a large number of diverse bacterial species showed that the elements of the control are generally found together and were detected in all species of Acinetobacter examined, as well as in a few other Gram-negative strictly aerobic bacteria.




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