Isolation and properties of Escherichia coli ATPase mutants with altered divalent metal specificity for ATP hydrolysis.

A method was devised for isolation of large numbers of energy-transducing ATPase (coupling factor) mutants based on a modification of the procedure of Hong and Ames (Hong, J. and Ames, B. N. (1971) Proc. Natl. Acad. Sci. U.S. 68, 3158-3162) for localized mutagenesis of any small region of the bacterial chromosome using transducing phages. The principle of this procedure is to mutate P1-transducing phage particles carrying the ATPase genes (Unc (uncoupled) DNA) using the strong chemical mutagen hydroxylamine. By transducing ilv- auxotrophs, a marker closely linked to Unc, to prototrophs, mutated Unc DNA can be introduced into the chromosome. We have used this method in conjunction with suitable selection procedures to isolate about 90 Unc- strains which have been classified by physiological, genetic, and biochemical criteria into three different phenotypes (Unc A, B, D). Mutants of the Unc D phenotype which were studied in detail were found to have the following properties: (1) aerobic growth yields on glucose are considerably lower than the wild type; growth occurs on glucose under anaerobic conditions; (2) Unc D lesions map near the ilv operon; (3) O2 uptake is comparable to the rate of wild type; (4) vesicles catalyze respiratory-dependent transhydrogenation, but show very low levels of Ca2+ ATP-dependent transhydrogenation; Mg2+ is ineffective; (5) oxidative phosphorylation is almost completely blocked irrespective of which metal ion is used; (6) the specific activity of ATPase is only about 20% of the wild type: (7) purified ATPase was found to have a marked specificity for Ca2+ as a divalent metal for ATP hydrolysis. A summary of properties of the new Unc mutants is discussed.