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ATP synthase Basics

Here is a brief description of this wonderful enzyme. If  you need more detailed general information see the FAQ list, or try wonderful lecture of A. Crofts (mirrored in University of Hamburg ).

This enzyme is the primary source of ATP in a vast majority of living species on Earth, including us. In human body it daily generates over 100 kg of ATP, which is subsequently used to provide energy for different biochemical reactions, including DNA and protein synthesis, muscle contraction, transport of nutrients and neural activity, to name just a few. In plants and photosynthetic bacteria it is essential for solar energy convertion and carbon fixation. This is one of the oldest enzymes on Earth, which appeared earlier then photosynthetic or respiratory enzyme machinery. This is a membrane enzyme. It is found in eu- and archebacteria in the plasma membrane; it is present in the thylacoid membrane in chloroplasts and in the inner mitochondrial membrane of eucariotic cells. Enzymes from different organisms show striking homology in the primary structure of subunits essential for catalysis. As could be deduced from the name of the enzyme, it catalyses the reaction of ATP synthesis/hydrolysis. The catalytic act is coupled with vectoral transmembrane translocation of several protons. The driving force for ATP synthesis is the transmembrane electrochemical gradient of protons, while during ATP hydrolysis this gradient is built using the energy of ATP phosphodietheric bond.

The overall equation is:

    ADP^3- + HPO₄^2- + H⁺ + nH⁺_out   <=>  ATP^4- + H₂O + nH⁺_in

where indices "out" and "in" denote the outer (positively charged) and the inner (negatively charged) side of the membrane, respectively.

The structure of this enzyme is rather sofisticated. It is an asymmetric multisubunit protein complex of about 500 kDa. It consists of two distinct (also in function) multisubunit portions. Hydrophobic F_o portion is embedded into the membrane and performs proton translocation, while hydrophillic F₁ portion protrudes into the aqueous phase and performs ATP synthesis/hydrolysis.
During catalysis a complex formed by certain subunits rotate relative to the rest of the enzyme. This feature makes ATP synthase the smallest rotary machine ever known.

ATP Links

• ATP and biological energy at Dr. Mike Farabee's webpage (Estrella Mountain Commuity College)
• ATP at Dr. Kimball's Biology Pages
• ATP: The Perfect Energy Currency for the Cell  by Dr. Jerry Bergman at  the True.Origin Archieve