ATP synthase dynamics and tentoxin binding probed using hybrid bacterial/chloroplast enzyme assemblies

摘要

The photosynthetic F_OF_1 ATP synthase couples the movement of protons down an electrochemical proton gradient to the synthesis of ATP. The enzyme is composed of a membrane-spanning proton channel (F_O) and a peripheral membrane sector (F_1) which contains the catalytic sites for reversible TP synthesis. The catalytic F_1 portion is comprised of five different polypeptide subunits designated alpha to epsilon in order of decreasing molecular weight with a stoichiometry of alpha_3 beta_3 gamma_1 delta_1 epsilon_1. Three catalytic sites, located primarily on the beta subunits at alpha beta subunit interfaces, interconvert between three different conformational states during ATP synthesis via energy-dependent affinity changes in substrate binding andproduct release (Boyer, 1997). Several recent studies of bacterial F_1 (Noji et al., 1997; Omote et al., 1999) and F_OF_1 (Sambongi et al., 1999; Panke et al., 2000) have suggested that this may be achieved by rotation of the gamma subunit relative to the alpha_3 beta_3 sub-assembly. Until now, rotational catalysis has not been convincingly demonstrated for the photosynthetic enzyme.