The Phosphoenolpyruvate Carboxykinase of Verticillium albo-atrum

Abstract

Partially purified phosphoenolpyruvate carboxykinase from Verticillium albo-atrum had a pH optimum of 6·2 and required manganese for maximum activity, having lesser activity with iron or cobalt. Sodium and potassium ions were slightly stimulatory. Adenosine-5′-diphosphate increased activity and inosine-5′-diphosphate supported low activity, but other nucleotides were ineffective. Inhibition of the enzyme by p-chloromercuribenzoate was partially reversed by dithiothreitol. Avidin had no effect on enzyme activity. Oxalacetate slightly stimulated the enzyme and NADP+ strongly inhibited, but aspartate and acetyl-CoA showed no effect. Low levels of phosphoenolpyruvate carboxykinase were present in cells grown on glucose, xylose, or glycerol. Aspartate, pyruvate, and acetate as carbon sources resulted in higher levels of activity and malate gave the highest. The data indicate that the enzyme functions physiologically in the gluconeogenic conversion of oxalacetate to phosphoenolpyruvate.