| Research Abstract |
Acetobacter methanolicus is a unique acetic acid bacterium which has a methanol oxidase respiratory chain, as seen in methylotrophs, in addition to its ethanol oxidase respiratory chain. In this study, the relationship between methanol and ethanol oxidase respiratory chains was investigated. Furhtermore, in this study, the structure and function of methanol dehydrogenase (MDH) purified from A. methatiolicus and alcohol dehydrogenases (ADH) purified from several acetic acid bacteria including A. metizanolicus. (1) A. methanolicus grown on methanol exhibited a high methanol oxidase activity and contained a cytochrome c oxidase, cytochrome co, while the cells grown on glycerol showed higher ethanol oxidase activity and contained an ubiquinol oxidase, cytochrome bo. The results obtained in this study suggest that A. methanolicus has two independent respiratory chains for methanol and ethanol. The methanol oxidase respiratory chain appears to operate by linking MDH to cytochrome c oxidase,
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cytochrome co, via soluble cytochrome(s) c, while the ethanol oxidase respiratory chain consists of ADH, ubiquinone and cytochrome bo ubiquinol oxidase. (2) Two different types of MDH were purified from A. methanolicus grown on methanol. One had an alpha2gamma2structure while the other did an alpha2gamma2 structure. Both types of enzyme had been detected in the periplasm at a ratio of 7 : 3, respectively. The results obtained here suggested that the alpha2gamma2 MDH may be produced from the alpha2gamma2 enzyme during the preparation. (3) ADH was purified from the membranes of glycerol-grown cells and shown to reduce ubiquinone-10 as well as a short side-chain homologue in detergent solution. The ethanol oxidase respiratory chain was reconstituted into proteoliposomes containing ADH together with ubiquinone-10 and cytochrome bo. Such a reconstitution has been established with ADHs purified from both Acetobacter aceti and Gluconobacter suboxydans. G. suboxydans ADH was dissociated into the subunit I, III and the subunit II, which were shown to be a quinohemoprotein dehydrogenase portion and diheme cytochrome c, respectively. Less
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