The role of the carbodiimide-reactive component of the adenosine-5'-triphosphatase complex in the proton permeability of Escherichia coli membrane vesicles

Abstract

Membrane vesicles isolated from wild-type and dicyclohexylcarbodiimide-resistant strains of Escherichia coli exhibit identical respiration-dependent transport activities, and in both cases, this activity is abolished by extraction of the vesicles with 1.0 M guanidine-HCl. Transport activity of extracted wild-type vesicles is completely restored by exposing the vesicles to lipophilic or water-soluble carbodiimides, while transport activity of the mutant vesicles is not restored by exposure to lipophilic carbodiimides. Strikingly, however, complete reactivation of transport in mutant vesicles is observed with water-soluble carbodiimides. Similarly, the Ca2+, Mg2+-stimulated ATPase activity of wild-type vesicles is inhibited by both classes of carbodiimides, while the ATPase activity of mutant vesicles is inhibited by water-soluble carbodiimides, but resistant to inhibition by lipophilic carbodiimides. The carbodiimide-reactive component of the membraneous Ca2+, Mg2+-stimulated ATPase complex in wildtype vesicles is readily labeled with N,N'-dicyclohexyl[14C]-carbodiimide, while the analogous component in mutant vesicles is not reactive. Alternatively, when vesicles are treated with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide [14C]methiodide, a water-soluble carbodiimide, the carbodiimide-reactive component is labeled to a similar degree in both preparations. The results suggest that the altered carbodiimide-reactive proteolipid in the dicyclohexylcarbodiimide-resistant mutant is specifically defective in its ability to react with lipophilic carbodiimides. In addition, these and other findings indicate that the increase in proton permeability observed on extraction of isolated membrane vesicles with chaotropic agents is due exclusively to an effect on the carbodiimide-reactive component of the Ca2+, Mg2+-stimulated ATPase complex.