Oxamate as a Differential Inhibitor of LactateDehydrogenase Isoenzymes

Oxamate is a non-competitive inhibitor of various lactate dehydrogenase preparations of human and animal origin when lactate is used as substrate. Its action on LD(1) (H(4)) is greater than that on LD(5) (M(4)), an effect which is most marked at a concentration about 3 mmol/1. Under these conditions the enzyme activity of a human heart extract is inhibited by about 50% while that of a human liver extract is reduced by only about 20%. The lactate dehydrogenase activities of a series of normal and pathological sera were determined in the presence or absence of oxamate. Those from patients with myocardial infarction were more sensitive to oxamate inhibition than those from patients with liver disease, but the differences observed were insufficiently great to warrant the use of oxamate as a differential inhibitor for clinical purposes.