The Pyruvate Carboxylase of Verticillium albo-atrum

Abstract

The pyruvate carboxylase of Verticillium albo-atrum had a pH optimum of 7·8 and a specific requirement for ATP. At the optimum pH, magnesium ions were required for maximum activity, while at pH 6·8 manganese was more effective than magnesium. Potassium was stimulatory while sodium was ineffective. Avidin and p-chloromercuribenzoate strongly inhibited the enzyme while biotin and dithiothreitol, respectively, reversed the effect of the inhibitors. Aspartate and oxalacetate were inhibitory while acetyl-CoA and CoA reversed the inhibition by aspartate. These cofactors were ineffective in the absence of aspartate. None of the tested metabolic intermediates was stimulatory to pyruvate carboxylase activity while NADP+ and 2,3-diphosphoglycerate were the most effective inhibitors (75%) at a concentration of 6·7 mM. Levels of pyruvate carboxylase in cells grown on glucose, acetate, malate, xylose, glycerol or aspartate differed only slightly. The data indicated that the physiological role of pyruvate carboxylase in V. albo-atrum is the anaplerotic biosynthesis of C4 Krebs-cycle intermediates from pyruvate.