Effect of metabolites of gamma-aminobutyric shunt on activities of NAD- and NADP-isocitrate dehydrogenases as well as aconitate hydratase from higher plants

摘要

We studied the influence of metabolites of gamma-aminobutyric shunt of the tricarboxylic acid cycle on the activities of aconitate hydratase (EC.4.2.1.3) as well as NAD- and NADP-specific isocitrate dehydrogenases (EC.1.1.1.41 and EC.1.1.1.42, respectively) using purified enzyme preparmions from pea leaves (Pisum sativum L.) and maize scutellum (Zea mays L.). gamma-Aminobutyric acid and succinate proved to have no significant effect on these enzymes, while 0.1-0.2 mM glutamate considerably activated NADP isocitrate dehydrogenase from the both sources, particularly, at unsaturating concentrations of the substrate. Succinic semialdehyde stimulated the activities of aconitate hydratase and NADP isocitrate dehydrogenase. The obtained data points to asimilar pattern of the effect of intermediates of gamma-aminobutyric shunt on the studied enzymatic activities for both photosynttietic tissues (pea leaves) and those with acidifying, transport, and digestive functions (maize scutellum). However, the absence of pronounced control effects of most metabolites on the studied enzymes allows us to assign them to a relatively inert pool of metabolites.