The F0F1-ATPase molecule is divided into two portions termed F1 and F0. The F0 portion is embedded in the thylakoid membrane, while the F1 portion projects into the lumen. Each portion is in turn made up of several different proteins or subunits. In F0, the subunits are named a, b, and c. There is one a subunit, two b subunits, and 9–12 c subunits. The large a subunit provides the channel through which H+ ions flow back into the stroma. Rotation of the c subunits, which form a ring in the membrane, is chemically coupled to this flow of H+ ions. The b subunits are believed to help stabilize the F0F1 complex by acting as a tether between the two portions. The subunits of F1 are called α, β, γ, δ, and ε. F1 has three copies each of α and β subunits which are arranged in an alternating configuration to form the catalytic “head” of F1. The γ and ε subunits form an axis that links the catalytic head of F1 to the ring of c subunits in F0. When proton translocation in F0 causes the ring of c subunits to spin, the γ–ε axis also spins because it is bound to the ring. The opposite end of the γ subunit rotates within the complex of α and β subunits. This rotation causes important conformational changes in the β subunits resulting in the synthesis of ATP from ADP and Pi (inorganic phosphate) and to its release.
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