Transduction of Electrochemical Ion Gradients to ATP Synthesis

Abstract

Proton pumping ATPases can be divided into three classes (Pedersen and Carafoli, 1987a,b; Nelson, 1988): (1) The eubacterial “F-type” that is present in bacteria such as E. coli, mitochondria, and chloroplasts, does not use a phosphorylated high-energy intermediate of the enzyme, and can function in both oxidative- and photo-phosphorylation to reversibly transduce $\Delta \tilde \mu _{{\text{H}}^ + }$ and ATP. (2) vacuolar “V-type” ATPases, found in the vacuolar systems of eukaryotic cells, and perhaps descended more directly from the archaebacteria, functions in acidification of the organelle interior. (3) The “P-type” is commonly found in the plasma membrane, utilizes a phosphorylated high-energy intermediate, and is also involved in the translocation of Na⁺, K⁺ and Ca²⁺. Most of the following discussion concerns the F-type used in organelle ATP synthesis. It is characterized by its multisubunit polypeptide composition. The notation EF₀ F₁, CF₀ F₁, MF₀ F₁, and TF₀ F₁ is used for the enzyme consisting of the membrane-bound (F₀) and peripheral (F₁ components from E. coli, chloroplasts, mitochondria, and thermophilic bacteria, respectively.