The activation of the cyclic-GMP phosphodiesterase via metarhodopsin I: a new model for vertebrate transduction.
Light-scattering spectrophotometry has been used to study rapid photo-induced molecular-cellular changes in vertebrate rod outer segments. Here, we discuss the temporal profiles of the nucleotide-independent P signal as a function of photobleaching, pH dependence in membrane-permeable and -impermeable buffers, angular and wavelength dependence, and cyclic-GMP phosphodiesterase inhibitors. On the basis of these observations, we suggest that (i) the P signal is coupled with the metarhodopsin I photo-intermediate and (ii) processes involved in the P signal invoke activation of cyclic-GMP phosphodiesterase. Furthermore, temperature-dependence studies indicate that the G protein does not participate in the scheme until the metarhodopsin II stage has been reached. This latter finding suggests that GTP-dependent processes are involved principally in the recovery of the system following light absorption. Our results point to a new model for phototransduction in vertebrate vision.
Deshpande
S
S
Department of Chemistry and Biochemistry, University of Guelph, Ont., Canada.
Abrahamson
E W
EW
D015106:3',5'-Cyclic-GMP Phosphodiesterases / Q000378:metabolism*; D000818:Animals; D002417:Cattle; D006863:Hydrogen-Ion Concentration; D008954:Models, Biological; D012168:Retinal Pigments / Q000502:physiology*; D012243:Rhodopsin / Q000031:analogs & derivatives / Q000502:physiology*; D015398:Signal Transduction
D012168:Retinal Pigments; C013110:metarhodopsins; D012243:Rhodopsin; D015106:3',5'-Cyclic-GMP Phosphodiesterases