The partial purification and characterization of the isoenzymes of malate dehydrogenase in the myxomycete Physarum flavicomum variety 1

The myxomycete Physarum flavicomum variety 1 was cultured in a semi-defined medium developed by Henney and Henney. When an aliquot of a crude extract of this organism was electrophoresed on polyacrylamide gel, two bands of malate dehydrogenase activity were observed. Since myxomycetes are eucaryotic organisms, these results indicated the possible existence of an intra- and extramitochondrial form of malate dehydrogenase. Both forms of malate dehydrogenase were partially purified. The two forms were then separated by successive column chromatography on carboxymethyl cellulose and further purified by gel filtration. The two isoenzymes were then characterized by a variety of physicochemical tests. These tests included the determination of inhibition by excess oxalacetate, heat stability, and Michealis constant values. A tentative identification of the intracellular location of the two forms of malate dehydrogenase was made. This identification was made primarily on the basis of the oxalacetate inhibition test.