Further studies on lactate dehydrogenase from serum of leukemic individuals

The kinetic properties of SLDH were investigated in untreated patients with acute leukemia at 37 degrees. SLDH was found to be inhibited by high pyruvate concentrations to a degree which depended on the pH of the reaction mixture; the degree of inhibition of normal SLDH at pH 7.5 was much higher than leukemic SLDH. 0.4M citrate was found to activate SLDH reaction rate at low pyruvate concentrations, while it was inhibitory at high pyruvate concentrations; the degree of inhibition being greater for leukemic SLDH than for normal SLDH. Citrate was also found to be a non-competitive inhibitor with respect to NADH and the value of Ki was determined. Methanol (3-4M), acted as a strong inhibitor to SLDH. The inhibition was found to be purely non-competitive with respect to pyruvate. Ki was calculated to be four times higher for leukemic SLDH than for normal SLDH.