Quinoprotein Alcohol Dehydrogenase of Acetic Acid Bacteria: Kinetic Study on the Enzyme Purified from Acetobacter methanolicus

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An alcohol delhydrogenase (ADH) complex consisting of subunits I, II, and III and the free subunit II were purified from Acetobacter methanolicus, The kinetic parameters of the purified ADH were investigated with several artificial electron acceptors. Simultaneous reactions with different electron acceptors showed that these electron acceptors competed with each other. Although free subunit II did not show any enzyme activity, part of the activity was restored after reconstitution with subunit I/III complex purified from Gluconobacter suboxydans. 2-n-Heptyl-4-hydroxyquinoline-N-oxide (HQNO) non-competitively inhibited all the reductase activities of native ADH, while the ferricyanide reductase activity of hybrid ADH was not inhibited by HQNO but the ubiquinone reductase activity was inhibited competitively. The kinetic study of native and hybrid ADHs suggests that at least three heme c moieties are involved in the reduction of ferricyanide and that the reduction of ubiquinone occurs in subunit II at a site different from the ferricyanide reacting site.