Organ specificity and lactate-dehydrogenase activity. 1. The relative activities with pyruvate and 2-oxobutyrate of electrophoretically separated fractions

Abstract

The nicotinamide-adenine dinucleotide-dependent isoenzymes of human and rabbit organ extracts which catalyse the reduction of 2-oxobutyrate have the same electrophoretic mobilities as the lactate-dehydrogenase isoenzymes of the same tissue. In both species the principal heart isoenzymes have greater electrophoretic mobilities at pH 8.6 than those of other tissues. They also show greater activity with 2-oxobutyrate relative to that with pyruvate than isoenzymes from other tissues. The principal liver isoenzymes exhibit little electrophoretic mobility at pH 8.6 and display low ratios for 2-oxobutyrate activity/pyruvate activity. Differences in the electrophoretic mobilities of the principal isoenzymes of human and rabbit skeletal muscle are paralleled by variations in the activity ratios. Evidence is presented to suggest that determination of the activity ratio is a convenient means of assessing the isoenzyme content of a given tissue.