Q9UII2

ATPases contain two linked complexes: F1, the hydrophilic catalytic core; and F0, the membrane-embedded protein channel. F1 consists of three α chains and three β chains, which are weakly homologous, as well as one γ chain, one δ chain and one ε chain. F0 consists of three subunits: a, b and c. A mitochondrial F1-ATPase inhibitor protein, ATPIF1 (ATPase inhibitory factor 1), also known as IP, IF1, ATPI or ATPIP (ATPase inhibitor protein), binds to the C-terminal region of a β subunit of the F1-ATPase at low pH values and, via interference of the β and γ subunit interaction, ATPIF1 regulates the activity of the F1F0-ATPase. This reversible ATPIF1 binding to F1F0-ATPase also occurs on the surface of endothelial cells.