Site of Interaction between Phenazine Methosulphate and the Respiratory Chain of Bacillus subtilis

Membrane vesicles from Bacillus subtilis W23 and from the menaquinone‐deficient Bacillus subtilis aroD were incubated with phenazine methosulphate and excess soluble phenazine methosulphate was subsequently removed by washing (preincubated vesicles). Phenazine methosulphate which remains attached to the membrane is accessible from the outer surface of the membrane because it can be reduced chemically by NADH or ascorbate and the reduced forms can mediate electrons to horse heart cytochrome c in the external medium of the membrane vesicles. The oxidation rates of ascorbate in preincubated vesicles of B. subtilis W23 and B. subtilis aroD and of NADH in preincubated vesicles of B. subtilis aroD increased with increasing amounts of phenazine methosulphate attached per mg membrane protein. Electrons from membrane‐attached reduced phenazine methosulphate are essentially all mediated to the terminal part of the respiratory chain before cytochrome a 601 because the oxidation of reduced phenazine methosulphate is almost completely inhibited by cyanide and only to a small extent by 2‐heptyl‐4‐hydroxy‐quinoline‐ N ‐oxide while NADH oxidase is strongly inhibited by both compounds. Furthermore, reduced phenazine methosulphate reduces completely cytochrome a 601 and not all cytochromes b 560 and c 553 . Active transport of amino acids is at least ten‐fold more effectively stimulated by NADH or ascorbate oxidation via phenazine methosulphate than by NADH oxidation via NADH dehydrogenase. Possible explanations are discussed.