Regulation of transducin GTPase activity in bovine rod outer segments

摘要: The photoreceptor G-protein, transducin, belongs to the class of heterotrimeric GTP-binding proteins that transfer information from activated seven-span membrane receptors effector enzymes or ion channels. Like other G-proteins, transducin acts as a molecular clock. It is by photoexcited rhodopsin which catalyzes exchange transducin-bound GDP for GTP and then stays active until bound hydrolyzed an intrinsic GTPase activity. Our previous study on components amphibian phototransduction cascade (Arshavsky, V. Y., Bownds, M. D. (1992) Nature 357, 416-417) has shown can be significantly accelerated target enzyme, cGMP phosphodiesterase (PDE), more specifically its gamma-subunit (PDE gamma). Here we report analogous mechanism present in bovine photoreceptors. Addition recombinant PDE gamma test membranes retain but are depleted endogenous causes significant acceleration A similar effect was observed with holoenzyme, not complex alpha- beta-subunits prepared limited proteolysis trypsin. activating increased concentration increases, exceeding 20-fold at concentrations over 80 microM approaching rate photoresponse turnoff. This suggests either contain further factor essential PDE-dependent regulation hydrolysis interact cooperative manner. We also GTPase-activating epitope located within C-terminal third gamma: peptide corresponding 25 amino acid residues accelerate almost well full-length gamma. part 3 residues: truncation mutant lacking these accelerates considerably less than whole length