Submicromolar Ag+ increases passive Na+ permeability and inhibits the respiration-supported formation of Na+ gradient in Bacillus FTU vesicles.
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+ (C1/2 = 1 x 10(-8) M or 2 x 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+.
Semeykina
A L
AL
Department of Bioenergetics, A.N. Belozersky Laboratory of Molecular Biology and Bioorganic Chemistry, Moscow State University, USSR.
Skulachev
V P
VP
D001407:Bacillus / Q000187:drug effects* / Q000502:physiology; D001693:Biological Transport, Active / Q000187:drug effects; D002414:Cations, Monovalent; D002463:Cell Membrane Permeability / Q000187:drug effects; D002474:Cell-Free System; D004734:Energy Metabolism / Q000187:drug effects; D006912:Hydroxyquinolines / Q000494:pharmacology; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D011808:Quinone Reductases / Q000378:metabolism*; D012834:Silver / Q000494:pharmacology*; D012964:Sodium / Q000378:metabolism*
D002414:Cations, Monovalent; D006912:Hydroxyquinolines; C001333:2-(n-heptyl)-4-hydroxyquinoline N-oxide; D012834:Silver; D012964:Sodium; C041831:NADH dehydrogenase (quinone); D011808:Quinone Reductases