Analysis of tryptophan mutants of F1-ATPase from Escherichia coli [Löbau et al. (1997) FEBS Lett. 404, 15–18] suggested that nucleotide concentrations used to grow crystals for the determination of the structure of bovine F1-ATPase [Abrahams et al. (1994) Nature 370, 621–628] would be sufficient to occupy only two catalytic sites, and that higher concentrations of nucleotide would result in all three sites being occupied. We have determined the structure of bovine F1-ATPase at 2.9 Å resolution with crystals grown in the presence of 5 mM AMPPNP and 5 μM ADP. Similar to previous structures of bovine F1-ATPase determined with crystals grown in the presence of lower nucleotide concentrations, only two β-subunits have bound nucleotide and the third subunit remains empty.
