Analysis of glycerol dehydrogenase activities present in <Emphasis Type="Italic">Mucor circinelloides</Emphasis> YR-1

Two inducible NADP⁺-dependent glycerol dehydrogenase (GlcDH) activities were identified in Mucor circinelloides strain YR-1. One of these, denoted iGlcDH2, was specifically induced by n-decanol when it was used as sole carbon source in the culture medium, and the second, denoted iGlcDH1, was induced by alcohols and aliphatic or aromatic hydrocarbons when glycerol was used as the only substrate. iGlcDH2 was found to have a much broader substrate specificity than iGlcDH1, with a low activity as an ethanol dehydrogenase with NAD⁺ or NADP⁺ as cofactor. Both isozymes showed an optimum pH for activity of 9.0 in Tris-HCl buffer and are subject to carbon catabolite repression. In contrast, the constitutive NADP⁺-dependent glycerol dehydrogenases (GlcDHI, II, and III) were only present in cell extracts when the fungus was grown in glycolytic carbon sources or glycerol under oxygenation, and their optimum pH was 7.0 in Tris-HCl buffer. In addition to these five NADP⁺-dependent glycerol dehydrogenases, a NAD⁺-dependent alcohol dehydrogenase is also present in glycerol or n-decanol medium; this enzyme was found to have weak activity as a glycerol dehydrogenase.