ATPsyntase

ATP synthase, also known as F-type ATP synthase, is a rotary enzyme that converts energy stored in a transmembrane proton gradient into chemical energy in the form of ATP. It is essential for cellular energy production in mitochondria and chloroplasts of eukaryotes and in many bacteria; a related enzyme family, V-type ATP synthases, uses ATP hydrolysis to pump ions and can function in the reverse direction under certain conditions. Some bacterial ATP synthases can use a sodium gradient instead of a proton gradient.

The enzyme consists of two linked sectors: Fo, the membrane-embedded proton channel, and F1, the soluble catalytic domain. The Fo portion contains a ring of proteolipid subunits that forms the rotor, and a stator that anchors to the membrane. The F1 domain sits in the cytoplasm or stroma and contains the catalytic α3β3 hexamer along with the central stalk composed of γ, δ, and ε subunits. The rotation of the central stalk inside the α3β3 ring couples proton flow to ATP synthesis.

Protons moving through Fo rotate the c-ring and the attached γ subunit. This mechanical rotation drives conformational changes in the β subunits of the F1 domain, converting ADP and inorganic phosphate into ATP in a binding-change mechanism often described as L, T, and O states. The process is a reversible rotary motor; ATP hydrolysis can drive proton pumping when cellular conditions require.

ATP synthase is vital for energy metabolism, producing most cellular ATP. It is a highly conserved enzyme across life and is a common target of inhibitors that disrupt proton flow or catalytic steps, reflecting its central role in bioenergetics.