The ATP synthase complex of Klebsiella pneumoniae (KF1F0) has been purified and characterized. SDS-gel electrophoresis of the purified F1F0 complexes revealed an identical subunit pattern for E. coli (EF1F0) and K. pneumoniae. Antibodies raised against EF1 complex and purified EF0 subunits recognized the corresponding polypeptides of EF1F0 and KF1F0 in immunoblot analysis. Protease digestion of the individual subunits generated an identical cleavage pattern for subunits alpha, beta, gamma, epsilon, a, and c of both enzymes. Only for subunit delta different cleavage products were obtained. The isolated subunit c of both organisms showed only a slight deviation in the amino acid composition. These data suggest that extensive homologies exist in primary and secondary structure of both ATP synthase complexes reflecting a close phylogenetic relationship between the two enterobacteric tribes.

The Fo complex of the ATP synthase (F1Fo) of Escherichia coli contains only two cysteinly residues, Cys21, of the two copies of subunit b. Modification of Cys21 with the hydrophobic maleimide N‐(7‐dimethylamino‐4‐methyl‐coumarinyl)maleimide resulted in impairment of Fo functions [Schneider, E. & Altendorf, K. (1985) Eur. J. Biochem. 153, 105–109]. We replaced this resdue (via cassette mutagenesis) by Ser, Gly, Ala, Thr, Asp and Pro. None of the replacements resulted in detectable alterations of the function of the ATP synthase, making a functional role for these sulfhydryl residues unlikely. Due to its high tolerance towards amino acid substitutions, the region around Cys21 seems not to be a protein‐protein contact area.