Malate dehydrogenase in Ascaris suum: Characterization, ontogeny, and genetic control

Whole body and tissue homogenates of Ascaris suum exhibit four major bands of malate dehydrogenase (MDH) activity by the method of starch gel electrophoresis: one, a cathodal form which predominates in mitochondria, and the other three, anodal forms which are located primarily in the supernatant fraction of the cells. Physico-chemical studies, including thermostability, pH optima, K_m's, substrate inhibition curves, and reactivity with coenzyme analogs demonstrated differences between the mitochondrial and supernatant enzymes similar to those reported for other species. In addition the three supernatant isozymes differed in their thermostability and pH optima curves, the middle isozyme exhibiting properties intermediate to those of the other two isozymes. Observations on the ontogeny and tissue distribution of the supernatant isozymes, dissociation and recombination experiments, and the detection of an electrophoretic variant suggest that Ascaris supernatant MDH isozymes are dimers composed of subunits under separate genetic control. The functional significance of the different forms of MDH in Ascaris is discussed.