Malate Dehydrogenase in Maize Endosperm: The Intracellular Location and Characterization of the Two Major Particulate Isozymes

Abstract

Multiple molecular forms of malate dehydrogenase (MDH) were detected in several tissues of maize using polyacrylamide gel electrophoresis. An investigation of MDH in 14-day-old endosperm tissue revealed that the two major isozymes were associated with particulate cell fractions, the mitochondria and glyoxysomes. Preparations of these two particulate isozymes, designated m-MDH and g-MDH, were obtained by anion-exchange chromatography and several physical and kinetic parameters were measured. Both isozymes had approximately the same Stokes radius (34 Å) but were catalytically distinct. Differences were found in their relative rates of reaction with NAD and two of its analogues (thionicotinamide-NAD and acetylpyridine-NAD) as well as in changes of Km (oxalacetate) with pH. The possible physiological roles of these two isozymes are discussed.