F 1 -ATPase (F 1 ) is the catalytic sector in F o F 1 -ATP synthase that is responsible for ATP production in living cells. In catalysis, its three catalytic b-subunits undergo nucleotide occupancy-dependent and concerted open-close conformational changes that are accompanied by rotation of the c-subunit. Bacterial and chloroplast F 1 are inhibited by their own e-subunit. In the einhibited Escherichia coli F 1 structure, the e-subunit stabilizes the overall conformation (half-closed, closed, open) of the b-subunits by inserting its C-terminal helix into the a 3 b 3 cavity. The structure of e-inhibited thermophilic F 1 is similar to that of E. coli F 1 , showing a similar conformation of the e-subunit, but the thermophilic e-subunit stabilizes another unique overall conformation (open, closed, open) of the b-subunits. The e-C-terminal helix 2 and hook are conserved between the two structures in interactions with target residues and in their positions. Rest of the e-C-terminal domains are in quite different conformations and positions, and have different modes of interaction with targets. This region is thought to serve e-inhibition differently. For inhibition, the e-subunit contacts the second catches of some of the b-and a-subunits, the N-and C-terminal helices, and some of the Rossmann fold segments. Those contacts, as a whole, lead to positioning of those b-and a-second catches in e-inhibition-specific positions, and prevent rotation of the c-subunit. Some of the structural features are observed even in IF 1 inhibition in mitochondrial F 1 .

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The eontractile system of striated (skeletal and cardiac) rnuscle has the autooscillation state called SPOC (SPontaneous Oscil]atory Centraction) state in addition to centraction and relaxation states (Ishiwata, S., Shimamoto, Y., Fukuda, N. {2011) Prog. Biophys. Mol. BioL, 105, 187-198.). This is observed at the intermediate levels of activation between contraction and relaxatien.