Malonate as a Participant in Organic Acid Metabolism in Bush Bean Leaves.

Interest in malonic acid has been largely directed towards its role as a competitive inhibitor of succinic dehydrogenase. Very little attention has been directed toward the occurrence of malonic acid in plants or toward the metabolismi of malonic acid per se. Bentley ( 1 ) recently showed malonate to be present in some 18 species of legumes, one of which had concentrations as high as 2 mg/g dry weight. Malonic acid has also been reported in species from families other than the legume family (1, 13, 20). That malonic acid could be metabolized was establishedl over 30 years ago when it was shown that malonate could serve as the sole carbon source for certain bacteria (3). More recent work established that malonate was readily metabolized by enzyme preparations from fungi (5, 6, 7, 10, 17, 18, 19), mammals (8, 11, 12), and peanut leaves (4). Recently Rhoads (16) and the present authors (21) reported that malonate was one of the major organic acids in bush bean leaves, often reaching levels as high as 10 mg/g dry weight. Incubation of malonate with a particulate preparation from bush bean leaf tissue suggested that malonate was metabolized. This paper describes experiments undertaken to study the metabolism of malonate in bush bean leaves, the cofactors required, and the pathway involvedl.