Microbial assimilation of methanol. The ethanol- and methanol-oxidizing enzymes of the yeast Candida boidinii.

Abstract

An NAD‐dependent alcohol dehydrogenase has been isolated from the yeast Candida boidinii grown on methanol. A study of the properties of the enzyme has shown that it is very similar to the alcohol: NAD oxidoreductase from baker's yeast. The alcohol dehydrogenase from Candida boidinii does not catalyze the oxidation of methanol and is constitutively formed. A mutant, 48, has been isolated which is unable to grow on methanol as sole carbon and energy source. This strain lacks the methanol‐oxidizing enzyme but not NAD‐dependent alcohol dehydrogenase. Cells grown on glucose or ethanol do not contain the methanol‐oxidizing enzyme. During adaptation from glucose to methanol, enzyme activity appears before growth on methanol begins. The methanol‐oxidizing enzyme has been partially purified. It catalyzes the oxidation of methanol to formaldehyde and hydrogen peroxide, and is independent of the addition of a hydrogen acceptor. The prosthetic group of this enzyme is FAD. The molecular weight was calculated to be 600000, one subunit has a molecular weight of 74000.The optima of pH and temperature for enzyme activity are 7.5–9.5 and 30°C, respectively. It is unstable in acidic pH.The enzyme is not specific for methanol. It also oxidizes lower primary alcohols. The Km value for methanol is 2.0 mM and that for ethanol 4.5 mM.