Summary: Glycerol : NAD 2-oxidoreductase (EC was purified to homogeneity from the non-methylotrophic yeast H 122. Results of electrophoresis in polyacrylamide gels, gel filtration and ultracentrifugation were compatible with the enzyme's consisting of two subunits with a molecular weight 38000. No heterogeneity was observed by isoelectric focusing. The pH optima were 10.0 for glycerol oxidation and 7.5 for dihydroxyacetone reduction. The values for glycerol, dihydroxyacetone, NAD and NADH were 5.8 × 10 M, 7.7 × 10 M, 1.4 × 10 M and 4.8 × 10 M, respectively. 1,2-Propanediol also served as substrate in the forward and DL-glyceraldehyde in the reverse reaction. The oxidation product of glycerol was identified as dihydroxyacetone. An ordered bi-bi mechanism was deduced from product-inhibition studies. Of several anions and cations tested, pyrophosphate and ammonium ions stimulated the dehydrogenating activity the most. 2-Mercaptoethanol, ethylene glycol and Tris inhibited activity; an inhibition was also observed by phosphorylated coenzymes and substrates. The purified enzyme, which is labile at low concentrations, was stabilized by the addition of neutralized filtrate from the culture liquid.


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