Pyruvate Decarboxylase from Zea mays L. : 2. Examination of Hysteretic Kinetics.

A significant lag phase was observed in the accumulation of product for the reaction catalyzed by pyruvate decarboxylase (PDC) purified from mature maize kernels. The effects of pH, pyruvate, potassium chloride, PDC concentration, and Mg(2+)-thiamine pyrophosphate upon this lag and upon the observed cooperativity were investigated. PDC preincubated with Mg(2+)-thiamine pyrophosphate for six days had Michaelis-Menten kinetics, a Hill number of 1, and no apparent lag phase. The degree of saturation of PDC with Mg(2+)-thiamine pyrophosphate appears to have a central role in controlling the lag phase and the degree of cooperativity.