Comparison of F1's of oxidative phosphorylation from Escherichia coli and Salmonella typhimurium and demonstration of interchangeability of their subunits.

The peripheral membrane portion (SF1) of proton-translocating ATPase of Salmonella typhimurium and its alpha, beta, and gamma subunits were purified and compared with the same portion (EF1) from Escherichia coli. The alpha, beta, and gamma subunits of these F1's were found to be mutually interchangeable, and all possible combinations of the three subunits from EF1 and SF1 showed ATPase activity. Both F1's could bind functionally to the integral membrane part (F0) of either bacterium, suggesting that F0 and F1 are interchangeable in these two bacteria and thus that the two F1's are closely similar at the level of subunit structure. However, SF1 differed from EF1 in some enzymological properties such as its specific activity and susceptibilities to sodium dodecyl sulfate and methanol. The specific ATPase activity of EF1 was more than twice that of SF1, and hybrid enzymes containing the beta subunit of EF1 had higher activity than other hybrids. Amino acid analysis suggested that the primary structures of the alpha subunits of the two F1's are less homologous than those of the beta subunits. Thus, the primary structure of the alpha subunit may be more species specific than that of the beta subunit.