SUBUNIT-II (B') AND NOT SUBUNIT-I (B) OF PHOTOSYNTHETIC ATP SYNTHASESIS EQUIVALENT TO SUBUNIT-B OF THE ATP SYNTHASES FROM NONPHOTOSYNTHETIC EUBACTERIA - EVIDENCE FOR A NEW ASSIGNMENT OF B-TYPE F-0 SUBUNITS

Subunit I of chloroplast ATP synthase is reviewed until now to be equi valent to subunit b of Escherichia coli ATP synthase, whereas subunit II is suggested to be an additional subunit in photosynthetic ATP synt hases lacking a counterpart in E. coli. After publication of some sequ ences of subunits II a revision of this assignment is necessary. Based on the analysis of 51 amino acid sequences of b-type subunits concern ing similarities in primary structure, isoelectric point and a discove red discontinuous structural feature, our data provide evidence that c hloroplast subunit II (subunit b' of photosynthetic eubacteria) and no t chloroplast subunit I (subunit b of photosynthetic eubacteria) is th e equivalent of subunit b of nonphotosynthetic eubacteria, and therefo re does have a counterpart in e.g. E. coli. In consequence, structural features essential for function should be looked for on subunit II (b ').