Abstract
Mechanisms of Na + transport into the inside-out subcellular vesicles of alkalo- and halotolerant Bacillus FTU and of Escherichia coli grown at different pH have been studied. Both microorganisms growing at pH 7.5 are shown to possess a system of the respiration-dependent Na + transport which (i) is inhibited by protonophorous uncoupler, by ΔpH-discharging agent diethylammonium (DEA) acetate, by micromolar cyanide arresting the H + -motive respiratory chain, and by amiloride, and (ii) is resistant to the Na + /H + antiporter monensin and to Ag + , inhibitor of the Na + -motive respiratory chain. Growth at pH 8.6 strongly changes the activator and inhibitor pattern. Now (1) protonophore stimulates the Na + transport, (2) DEA acetate is without effect in the absence of protonophore and is stimulating in its presence, (3) amiloride and low cyanide are ineffective, (4) monensin and Ag + completely arrest the Na + accumulation in the vesicles. Independent of pH of the growth medium, (a) valinomycin is stimulatory for the Na + transport, (b) Na + ionophore ETH 157 is inhibitory and, (c) Na + transport can be supported by NADH → fumarate as well as by ascorbate (TMPD) → O 2 electron transfers. Growth at alkaline pH results in the appearance of ascorbate (TMPD) oxidation resistant to low and sensitive to high cyanide concentrations. These relationships are in agreement with the concept (Skulachev, V.P. (1984) Trends Biochem. Sci. 9, 483–485) that adaptation to alkaline conditions in bacteria growing in the high [Na + ] media causes substitution of Na + for H + as a coupling ion. The obtained data indicate that under alkaline conditions, Na + can be pumped from the cell by the Na + -motive respiratory chain with neither H + -motive respiration nor the Na + /H + antiporter involved. In the Na + -motive respiratory chain of Bac. FTU or E. coli , two Na + pumps are localized, one in its initial and the other in its terminal spans.
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Schedule a callMore From: Biochimica et Biophysica Acta (BBA) - Reviews on Bioenergetics
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