Effect of uncoupler on “Downhill” substrate efflux of Escherichia coli is dependent on (Mg2+,Ca2+)· adenosine triphosphatase
✍ Scribed by Boris Rotman
- Publisher
- John Wiley and Sons
- Year
- 1976
- Tongue
- English
- Weight
- 403 KB
- Volume
- 89
- Category
- Article
- ISSN
- 0021-9541
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✦ Synopsis
Abstract
Previous studies have shown that mutations in the unc gene of Escherichia coli K12 cause defects in energy transduction as well as in a membrane‐bound (Mg^2+^,Ca^2+^)· adenosine triphosphatase.
We studied the effect of this mutation on the “downhill” efflux of methyl‐β‐D‐galactopyranoside, a substrate of the mgl transport system. While unc^+^ and unc^−^ isogenic strains of E. coli K12 did not show significant differences in substrate influx or efflux, a differential effect of an uncoupler, 2,4‐dinitrophenol was demonstrated. In contrast to the unc^+^, dinitrophenol failed to inhibit significantly the rate coefficient of efflux in the unc^−^ strain.
Analyses of spontaneous unc^+^ revertants of the unc^−^ mutant provided additional evidence that a functional unc gene is necessary for dinitrophenol inhibition of efflux.
Other uncouplers tested in the unc^+^ strain showed different effects on efflux. While arsenate, azide and carbonyl cyanide p‐trifluoromethoxyphenylhydrazone caused little or no effect, 2,4‐dibromophenol and pentachlorophenol increased efflux by a considerable factor.