In the crystal structure of bovine mitochondrial F1-ATPase determined at 2.8 A resolution, the three catalytic beta-subunits differ in conformation and in the bound nucleotide. The structure supports a catalytic mechanism in intact ATP synthase in which the three catalytic subunits are in different states of the catalytic cycle at any instant. Interconversion of the states may be achieved by rotation of the alpha 3 beta 3 subassembly relative to an alpha-helical domain of the gamma-subunit.

The a-and ,B-subunits of membrane-bound ATP synthase complex bind ATP and ADP: B contributes to catalyic sites, and a may be involved in regulation of ATP synthase activity. The sequences of ,B-subunits are highly conserved in Escherichia coli and bovine mitochondria. Also a and ( are weakly homologous to each other throughout most of their amino acid sequences, suggesting that they have common functions in catalysis. Related sequences in both a and (3 and in other enzymes that bind ATP or ADP in catalysis, notably myosin, phosphofructokinase, and adenylate kinase, help to identify regions contributing to an adenine nucleotide binding fold in both ATP synthase subunits.

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