| Abstract | Transport of L-alanine and AIB into isolated membrane vesicles of marine pseudomonad B-16 (ATCC 19855) was stimulated by NADH and ascorbate-TPD. Other electron donors tested and ATP had no stimulatory effect. The uptake of both amino acids required Na+ specifically. Neither Li+, K+ nor Rb+ could replace Na+ for transport. Using L-alanine as the test amino acid, it was found that both endogenous transport and NADH stimulated transport was inhibited by anaerobiosis, HOQNO and CN−. Transport in the presence of ascorbate-TPD was inhibited by anaerobiosis and by CN− but not by HOQNO. PEA induced the loss of L-alanine from membrane vesicles which had been allowed to accumulate the amino acid, suggesting that L-alanine had been concentrated inside the vesicles against a gradient. Thus, the Na+-dependent transport process is an active one and is coupled to the oxidation of electron donors. The site of energy coupling appears to lie below the quinone in the respiratory chain. |
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