Oxaloacetate acetylhydrolase activity in virulent and hypovirulent strains of Endothia (Cryphonectria) parasitica

Abstract

Extracts of three virulent strains of Endothia (Cryphonectria) parasitica and three hypovirulent strains derived from them were assayed for enzyme activities that would produce oxalate. Oxaloacetate acetylhydrolase (E.C. 3.7.1.1), the enzyme that converts oxaloacetate to oxalate and acetate, was at least four times higher in extracts of the virulent strains than in extracts of the hypovirulent strains. The level of activity of this enzyme could account for the formation of all the oxalate produced by the virulent cultures. When extracts of hypovirulent strains were added to extracts of virulent strains, the measured rate was less than the sum of the two rates. The inhibition did not change when the hypovirulent extract was either dialysed or boiled. No enzyme activity for the conversion ofglycolate or glyoxylate to oxalate could be detected in any of the extracts.

There was no apparent difference between the virulent and hypovirulent strains of the fungus on the basis of intracellular organic acid content except that fumarate concentration was lower in extracts of hypovirulent strains. The amounts of oxalate produced by the virulent strains when grown on solid medium with malate (an immediate precursor of oxaloacetate) and fumarate were much higher than when they were grown on solid medium with glycolate. Two of the hypovirulent strains produced no oxalate on any of the substrates. However, the hypovirulent strain which had the highest oxaloacetate acetylhydrolase activity produced oxalate cultured on malate and fumarate but none on glycolate.