ATP Synthase – an Example for Chemical Energy Regulated Protein
ATP synthase is enzyme located mainly in mitochondrial inner membrane and bacterial plasma membrane, coupled with the proton concentration gradient developed by electron transport chain carrying the synthesis of ATP from ADP and inorganic phosphate. The molecular mass of ATP synthase is around 550. The difference in molecular mass is due to different stoichiometry arrangements of subunit c, whose number ranges from 8 to 15.
In Lehninger: Principles of Biochemistry, the author point out the functions of protein rise from three classes: a, reversible binding of protein and ligands, which involves induced fit; b, complementary interaction between protein and ligands, which is dominated by stereochemistry and non-covalent interactions; c, interactions of protein and ligands are regulated by chemical energy, where the energy is mainly consumed in conformational change of proteins. ATP synthase is an elegant example for the last point, where energy stored in electro-chemical potential of proton is finally converted into chemical energy in ATP molecules with the help of a sophisticated and well-organized mechanism.
ATP synthase is organized with two fragments, F1 and Fo. F1 is peripheral in the mitochondrial matrix side, consisting of three α and three β subunits as well as one γ, δ and ε subunit. The shape of F1 is like a knob: alternating arranged α and β subunits form a spherical hexamer, with γδε complex probed into its axis using two long helices of γ. Fo is integrated in mitochondrial inner membrane. 8 to 10 c subunits form a cylindrical ring perpendicular to the membrane, with one a subunit attached by them. Single b subunit form a long holder, fusing the a subunit and one certain β subunit in F1 together. The ε subunit associates the c ring with the γδε shaft.
In general point of view, the mechanism