INDUCTION OF THE ESCHERICHIA-COLI CYTOCHROME-D BY LOW DELTA(MU)OVER-BAR(H-IONS() AND BY SODIUM)

Regulation of synthesis of cytochrome d in Escherichia coli has been s tudied using mutants with cytochrome-d-beta-galactosidase gene fusions . It was shown that various protonophorous uncouplers, when added to t he growth medium, cause induction of the cytochrome d synthesis. The c ytochrome-d-inducing activity of uncouplers correlates with their abil ity to inhibit such a Delta<(mu)over bar>(H+)-driven function as motil ity of the E. coli cells. An increase in the Na+ concentration in the growth medium from 1.5 mM to 25 mM results in induction of the cytochr ome d synthesis. The cytochrome-d-inducing effect of uncouplers is muc h more pronounced when the Na+ concentration is high than when it is l ow. These data are in agreement with the assumption that cytochrome d is involved in the Na+ energetics substituting for the H+ energetics w hen the latter appears to be inefficient. Mutations in arcA or arcB ge nes (but not in fnr gene) completely prevent the increase in the cytoc hrome d level induced by uncouplers but are without effect on that ind uced by Na+. It is assumed that in the control of the cytochrome d syn thesis, the Are system is involved in the Delta<(mu)over bar>(H+) sens ing whereas sensing of Delta<(mu)over bar>(Na+) (or of the Na+ concent ration) is mediated by some other receptor system.