Polyol dehydrogenase of the silkworm

Abstract

Dialysed hemolymph of the silkworm, Bombyx mori L. contains a triphosphopyridine nucleotide-linked polyol dehydrogenase that reduced glycolaldehyde to ethylene glycol, DL-glyceraldehyde to glycerol and D-erythrose to erythritol. Among the other hydroxyaldehydes and carbonyl compounds reduced by the enzyme preparation are D-threose, glucuronic and galacturonic acids, ribose 5-phosphate, glyoxal, methylglyoxal and dimethylglyoxal. Hexoses and pentoses are not reduced and dihydroxyacetone is reduced at 5% of the rate for D-glyceraldehyde. The equilibrium of the reaction favors the reduction of the carbonyl compounds at pH 7.5; but the oxidation of butane-2:3 diol, propylene glycol and glycerol in the presence of triphosphopyridine nucleotide can be demonstrated at high substrate concentration (M) ["M" order of magnitude, 1000 times the usual MM concentrations] at pH 8.5. The enzyme oxidizing the glycols is distinct from the "malic" enzyme of the hemolymph, but the reduction of glyceraldehyde and ribose 5-phosphate appears to be catalyzed by the same protein fraction. Polyol dehydrogenase was detected in extracts of the fat body and the gut of larvae, and in extracts of whole pupae and adults.