Phosphodiesterase and GTPase in rod outer segments. Kinetics in vitro.
Biochim Biophys Acta, 1979/2/19;583(1):1-13.
Caretta A, Cavaggioni A, Sorbi RT
PMID: 217445
Abstract
The hydrolysis of cyclic guanosine monophosphate (cyclic GMP) and of guanosine triphosphate (GTP) by the broken rods of the frog retina after a flash of light have been studied in vitro with a constant perfusion method. The activation has an onset apparently instantaneous as observed with the existing possible time resolution of 3 s. The activation is followed by a partial inactivation that does not bring the activity back to the pre-flash level. GTP or the non-hydrolysable guanyl-5'-ylimidodiphosphate (GMP-PNP) is required for the normal light-activation of the phosphodiesterase and in its absence both the speed of activation and the sensitivity are greatly reduced. The activation speed, the sensitivity (threshold at approx. 0.00004% bleaching), and the kinetic constants do not exclude a direct role in the process of excitation for the phosphodiesterase and suggest a subsidiary but as yet undefined role for the GTPase.
MeSH terms
3',5'-Cyclic-GMP Phosphodiesterases; Animals; Anura; Cyclic GMP; Darkness; Dose-Response Relationship, Radiation; GTP Phosphohydrolases; Guanosine Triphosphate; Guanylyl Imidodiphosphate; Kinetics; Light; Phosphoric Diester Hydrolases; Phosphoric Monoester Hydrolases; Photoreceptor Cells; Rana esculenta
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