OBSERVATIONS ON THE HETEROGENEITY OF MALIC AND LACTIC DEHYDROGENASE IN HUMAN SERUM AND RED BLOOD CELLS1

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Abstract
Human serum separated electro-phoretically exhibited 3 regions of malic dehydrogenase (MDH) activity. In 10 control subjects the percentage of MDH activity in each peak remained relatively constant, although the total activity in serum varied widely. Hemolysates from red cells separated electro-phoretically revealed three peaks of dehydrogenase activity similar to those found in serum. The MDH activity peaks in the [alpha]2-globulin and between the a1-globulin and albumin corresponded in mobility and in pH optima to the lactic dehydrogenase (LDH) activity found in the same regions. Alteration in the electrophoretic conditions thus far employed have failed to separate the proteins acting on these substrates in the two activity peaks. However, the LDH activity peak in the B-globulin differed from the MDH activity peak, both in electrophoretic mobility and pH optima. The similarities between the [alpha]2 activity peaks of MDH and LDH raise the question of whether the [alpha]2 peaks may be due to a single protein which can act on either substrate. Similarly, the possibility that the [alpha]1 peaks of MDH and LDH activity may also be produced by one enzyme is discussed. Further studies will be required to settle these questions It is suggested that the multiplicity of the dehydrogenase enzymes in serum should be considered in evaluating observations of total enzymatic activity in disease states.