Purification and Properties of Two Different Dihydroxyacetone Reductases inGluconobacter suboxydansGrown on Glycerol

It is well known that in oxidative fermentation microbial growth is improved by the addition of glycerol. In a wild strain, glycerol was converted rapidly to dihydroxyacetone (DHA) quantitatively in the early growth phase by the action of quinoprotein glycerol dehydrogenase (GLDH), and then DHA was incorporated into the cells by the early stationary phase. Two DHA reductases (DHARs), NADH-dependent (NADH-DHAR) (EC 1.1.1.6) and NADPH-dependent (NADPH-DHAR) (EC 1.1.1.156), were detected in the same cytoplasm of Gluconobacter suboxydans IFO 3255. The former appeared to be inducible and labile in nature while the latter was constitutive and stable. The two DHARs were separated each other and were finally purified to crystalline enzymes. This report might be the first one dealing with NADPH-DHAR that has been crystallized. The two DHARs were specific only to DHA reduction to glycerol and thus contributed to cytoplasmic DHA metabolism, resulting in an improved biomass yield with the addition of glycerol.