Catalytic properties of three L-lactate dehydrogenases from saffron corms (Crocus sativus L)

Three L-lactate dehydrogenase isoenzymes were detected in saffron corms, using potassium ferricyanide as the electron acceptor. Their pH optima were 5.5, 7.5 and 9.5, respectively. All three dehydrogenases were substrate-inhibited by ferricyanide, but at different concentrations; maximum enzymatic activity was observed for 250, 100 and 600 microM ferricyanide, at pH 5.5, 7.5 and 9.5, respectively. Catalytic efficiency, calculated per mg corm extract protein, was 1.9, 1.0 and 0.4 min(-1), respectively at pH 5.5, 7.5 and 9.5. Pseudo first order rate constant was also different under the three pH conditions. Malate was an inhibitor for the isoenzyme active at pH 9.5, but had no effect on the others.