Isolation and Properties of a Pyruvate Dehydrogenase Complex from the Yeast Hansenula miso

Abstract

A pyruvate dehydrogenase complex (PDC) was isolated from the yeast Hansenula miso and shown to have a sedimentation coefficient (s°_{20, w}) of 50.7S. It catalyzed the oxidation of pyruvate at a rate of 7.4μmoles per min per mg protein. The oxidation activity was absolutely dependent on coenzyme A, NAD⁺, and thiamine pyrophosphate (TPP) and partially dependent on Mg²⁺. The enzymatic reaction proceeded optimally at pH 8.2. The K_m value for pyruvate was determined to be 0.16mM. In addition to pyruvate, α-ketobutyrate and α-ketovalerate were also oxidized by the enzyme preparation, though the activity towards the latter compound was low. The purified PDC preparation also catalyzed the synthesis of α-acetolactate from pyruvate as well as the synthesis of acetoin from pyruvate plus acetaldehyde.