Identification of an uncoupling mutation affecting the b subunit of F₁F₀ ATP synthase in Escherichia coli

A specific b subunit arginine, b(Arg-36) in Escherichia coli, displays evolutionary conservation among bacterial F₁F₀ ATP synthases. Site- directed mutagenesis was used to generate a collection of mutations affecting b(Arg-36). The phenotype differed depending upon the substitution, and the b(Arg-36→Glu) and b(Arg-36→Ile) substitutions virtually abolished enzyme function. Although the total amounts of F₁F₀ ATP synthase present in the membranes prepared from mutant strains were reduced, the primary effect of the b(Arg-36) substitutions was on the activities of the intact enzyme complexes. The most interesting result was that the b(Arg-36-Glu) substitution results in the uncoupling of a functional F₀ from F₁ ATP hydrolysis activity.