Abstract
Three types of isocitrate dehydrogenase were partially purified from a single source, beef heart muscle, and their enzymatic pro-perties were compared. Two types of the NADP-linked dehydrogenase, one of which was isolated from mitochondria and the other from soluble fraction, have almost the same properties in their optimum pH of the enzyme actions and in affinities to their substrate and cofactors. But some of heavy metal ions (Hg++, Cd++ and Cu++), arsenite and PCMB inhibited these enzyme activities differently. Moreover these enzymes showed a quantitative difference in metal ion (Mg++/Mn++) requirement. Dis-tinguishable properties of the NADP-linked enzymes and the NAD-linked enzyme were also confirmed.
