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KMID : 0545119960060060391
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Journal of Microbiology and Biotechnology
1996 Volume.6 No. 6 p.391 ~ p.396
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Na^+-dependent NADH:quinone Oxidoreductase in the Respiratory Chain of the Marine Bacterium Marinomonas vaga
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KIM YOUNG-JAE
PARK YONG-HA
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Abstract
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The Gram-negative marine bacterium Marinomonas vaga, which requires 0.5 M NaCl concentration for optimal growth, is slightly halophilic. The growth of M. vaga was highly resistant to the proton conductor, carbonyl cyanide m-chlorophenylhydrazone (CCCP) under alkaline pH conditions (pH 8.5) but very sensitive to CCCP under acidic pH conditions (pH 6.5). These results suggest that the respiratory chain-linked NADH oxidase system of M. vaga may lead to generation of a Na^+ electriochemical gradient. In order to examine the existence of Na^+-stimulated NADH oxidase in M. vaga, membrane fractions were prepared by the osmotic lysis method. The membrane-bound NADH oxidase oxidized both NADH abd deamino-NADH as substrates and requird Na^+ for maximum activity. The maximum activity of NADH oxidase was obtained at about pH 8.5 in the presence of 0.2 M NaCl. The site of Na^+-dependent activation in the NADH oxidase system was at the NADH: quinone oxidoresuctase segment. The NADH oxidase and NADH: quinone oxidoresuctase were very seneitive to the respiratory chain inhibitor, 2-heptyl-4-hydroxyquinoline-N-oxide (HQNO) in the presence of 0.2 M NaCl but highly resistant to another respiratory inhibitor, rotenone. Based on these findings, we conclude that M. vaga possesses the Na^+-dependent NADH: quinone oxidoresuctase that may function as an electrogenic Na^+ pump.
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