Distinct physiological roles of two membrane-bound dehydrogenases responsible for D-sorbitol oxidation in Gluconobacter frateurii
Soemphol, W.(Yamaguchi Univ. (Japan). Faculty of Agriculture) | Adachi, O. | Matsushita, K. | Toyama, H.
Two different membrane-bound enzymes oxidizing D-sorbitol are found in Gluconobacter frateurii THD32: pyroloquinoline quinone-dependent glycerol dehydrogenase (PQQ-GLDH) and FAD-dependent D-sorbitol dehydrogenase (FAD-SLDH). In this study, FAD-SLDH appeared to be induced by L-sorbose. A mutant defective in both enzymes grew as well as the wild-type strain did, indicating that both enzymes are dispensable for growth on D-sorbitol. The strain defective in PQQ-GLDH exhibited delayed L-sorbose production, and lower accumulation of it, corresponding to decreased oxidase activity for D-sorbitol in spite of high D-sorbitol dehydrogenase activity, was observed. In the mutant strain defective in PQQ-GLDH, oxidase activity with D-sorbitol was much more resistant to cyanide, and the Hsup(+)/O ratio was lower than in either the wild-type strain or the mutant strain defective in FAD-SLDH. These results suggest that PQQ-GLDH connects efficiently to cytochrome bosub(3) terminal oxidase and that it plays a major role in L-sorbose production. On the other hand, FAD-SLDH linked preferably to the cyanide-insensitive terminal oxidase, CIO.
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