The Reduction of 5-oxodecanoic Acid by Normal Baker's Yeast.

1. A description is given of the course of the reduction of 5-oxodecanoic acid to 5-hydroxydecanoic acid by intact cells of baker's yeast and of the influence of pH on this reduction. As the pH of the medium is decreased the rate of uptake of the keto acid by yeast increases. However, the more the rate of uptake increases the more rapidly the yeast is poisoned by the keto acid or hydroxy acid or both. Consequently the optimum pH is at approx. 5. 2. In baker's yeast the conversion of 5-oxodecanoic acid takes place mainly in the mitochondria. 3. The conversion is strongly influenced by ATP, NADPH and Mg(2+) or Mn(2+), and to a smaller extent by CoA.SH. The NADP can only partly be replaced by NADH. Thus the reduction seems to be NADPH-dependent. A mechanism for the conversion is proposed. 4. Like the reduction by intact cells, the reduction by an isolated mitochondrial fraction proceeds stereospecifically.