Submicromolar Ag+ increases passive Na+ permeability and inhibits the respiration‐supported formation of Na+ gradient in Bacillus FTU vesicles

[摘要]

The effect of Ag⁺ on Na⁺ pumping by Na⁺-motive NADH-quinone reductase and terminal oxidase has been studied in Bacillus FTU inside-out vesicles. Very low concentrations of Ag⁺ (C = 1 × 10⁻⁸M or 2 × 10⁻¹² g ion · mg protein⁻¹) are shown to inhibit the uphill Na⁺ uptake coupled to the oxidation of NADH by fumarate or of ascorbate + TMPD by oxygen but exert no effect on the H⁺ uptake by the H⁺-motive respiratory chain. Low Ag⁺ also induces a specific increase in the Na⁺ permeability of the vesicles. HQNO, added before and not after Ag⁺, prevents the Ag⁺-induced permeability increase, with effective HQNO concentrations being similar to those inhibiting the uphill Na⁺-uptake coupled to the NADH-fumarate oxidoreduction. Reduction of terminal oxidase by ascorbate + TMPD in the presence of cyanide sensitizes the Na⁺ permeability to Ag⁺. It is suggested that low [Ag⁺], known as a specific inhibitor of electron transport by the Na⁺-motive NADH-quinone reductase, uncouples the electron and Na⁺ transports so that the Ag⁺-modified NADH-quinone reductase operates as an Na⁺ channel rather than an Na⁺ pump. This effect is discussed in connection with the antibacterial action of Ag⁺.

[学科分类] 生物化学/生物物理

[关键词] Bacterial sodium energetics;Silver;NADH-quinone reductase;Terminal oxidase;CCCP;carbonyl cyanide m-chlorophenylhydrazone;DEA;diethylamine;HQNO;2-heptyl-4-hydroxyquinoline N-oxide;TMPD;N;N;N';N' -tetramethyl p-phenylene diamine;TPT;triphenyltin acetate