Dehydrogenase Activity of Hydroxymalonate and Related Acids in Higher Plants

Abstract

A dehydrogenase activity capable of a reversible conversion of hydroxymalonate (tartronate) to ketomalonate (mesoxalate) in the presence of diphosphopyridine nucleotide has been demonstrated in a variety of plant extracts. An 80-fold purification of the enzyme was made. Although oxalacetate and diketosuccinate activities were still present, changes in relative activity occurred indicating that different enzymes are involved. Furthermore, hydroxymalonate is a competitive inhibitor of malic dehydrogenase activity at enzyme concentrations too weak to give any activity with hydroxymalonate alone. Possible relationships with D-tartrate, dihydroxyfumarate, and diketosuccinate are discussed. Methods to distinguish hydroxymalonate from tartaric acid are presented.