Characterization of Malate Dehydrogenase Isozymes in Wheat Germ

Malate dehydrogenase of wheat germ exists in multiple molecular forms (isozymes). Comparisons of some physical properties such as Stoke's radii, sedimentation constants, electrophoretic mobilities on polyacrylamide gel, chromatographic behaviors on DEAE-cellulose, stabilities to heat and iodacetamide inactivation, as well as kinetic parameters were described. When all these properties are considered together, at least five isozymes were found to associate with cytoplasm, mitochondria, glyoxysomes and proplastids of wheat germ. Wheat germ malate dehydrogenases are specific for the reduction of oxaloacetate and its monoesters. At least one carboxylic group of oxaloacetate must be free, in order to exhibit substrate activity, and maximum binding of oxaloacetate is achieved when both carboxylic groups are free. Soluble malate dehydrogenase and organelle-associated malate dehydrogenase can be differentiated readily in that the former can not utilize 4-ethyl oxaloaceode of ATP inhibition.