Inhibition studies on LDH isoenzyme purified from Uromastix testes

An LDH isoenzyme was purified to homogeneity from uromastix testes and its inhibition spectrum towards known LDH isoenzyme inhibitors studied. Platinum compounds inhibited the enzyme in the forward reaction (pyruvate-->lactate) only, n-hexanediol and colchicine showed no inhibition and gossypol acetic acid (GAA) strongly inhibited both the forward and reverse reactions and the reactions were time-dependent. Oxalate caused non-competitive inhibition (Ki app = IC50 = 0.15 mM) of the forward reaction, NADH was more effective in blocking inhibition by GAA than pyruvate. This enzyme was also unable to use ketocaproic acid as a substrate.