Properties of Yeast Pyruvate Decarboxylase and their Modi - fication by Proteolytic Enzymes

Pyruvate decarboxylase has been shown to be more heat labile in extracts of a mutant strain than in extracts of the parent yeast strain. Mutant extracts were found to contain higher levels of proteolytic enzymes than wild-type extracts, although aging of the latter preparations resulted in the activation of inactive pmteases. A partially purified protease preparation was shown to degrade pyruvate decarboxylase in a selective manner such that the ability to form free acetaldehyde was destroyed while the acetylmethylcarbinol-forming activity was increased 60’,-. Pyruvate, or a mixture of pyruvate and acetaldehyde, was partly successful in protecting pyruvate decarboxylase from the action of the protease. Stabilization of pyruvate decarboxylase by high concentrations of phosphate, sulfate, or glycerol has been shown to be due to the inhibitory action of these compounds on yeast proteases. Pyruvate decarboxylase which was partially degraded by the protease had different relative activities on a series of a-keto acids from the corresponding activities of a nondegraded decarboxylase preparation. The data presented are in accord with a two-site mechanism postulated for pyruvate decarboxylase.