The functional role of thiol groups of pyruvate decarboxylase from brewer's yeast.

Pyruvate decarboxylase purified from brewer's yeast has been modified by the thiol specific reagents 4-hydroxy-mercuri-benzoate and 3-bromo-pyruvamide. The kinetic properties of the thiol-modified enzyme derivatives were investigated by stopped-flow technique. The enzyme--inactive in the absence of its substrate--is activated by binding pyruvate to the regulatory sites. This activation behaviour is lost after modification of six thiol groups per PDC molecule. The thiol groups have been subdivided into two classes according to their modification rates. Two of these six thiol groups are involved in the mechanism of enzyme activation.