1,720,972 research outputs found
Phosphodiesterase and GTPase in rod outer segments kinetics in vitro
No full textThe 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 levl. GTP or the nonhdrolysable 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. © 1979
Search for a physiological role of cyclic GMP metabolism in the photoreceptors
No full textData on the time-course of the light-activation of the cyclic GMP phosphodiesterase and of the GTPase, and results on the influence of cyclic GMP on the disc membrane permeability are presented. On the basis of the kinetic data, it is not possible to separate the light-activation of these two enzymes from the early steps of photoreceptor transduction. In addition, the cyclic GMP increases the permeability of the disc membranes, indicating that a decrease of the endogenous cyclic GMP concentration, consequent to the light-activation of the phosphodiesterase, can decrease the membrane permeability shortly after illumination. © 1980
Cyclic GMP and the permeability of the disks of the frog photoreceptors
No full text1. The diffusion of sodium, potassium and rubidium (not chloride) ions across the disk membrane is increased by cyclic guanosine monophosphate (cyclic GMP). 2. The increase is greater for sodium than for rubidium in the 0.01‐0.1 mM concentration range. 3. Cyclic adenosine monophosphate (cyclic AMP) is less efficient than cyclic GMP; GMP and guanosine triphosphate are without effect. 4. The effect is present with either 1.8 mM calcium ions or 4 mM‐EGTA in the perfusion fluid. 5. The presence of the cyclic GMP phosphodiesterase on the disk membranes is not needed for this effect. 6. The effect is present in both unbleached and fully bleached membranes. © 1979 The Physiological Societ
Binding stoichiometry of a fluorescent cGMP analogue to membranes of retinal rod outer segments
No full textThe high‐affinity binding of the cGMP analogue 8‐(5‐thioacetamidofluorescein)‐cGMP to rod outer segment membranes depleted of peripherally bound proteins has been defined by equilibrium dialysis (mean ± SD): (a) membranes contain about one cGMP binding site per 130 rhodopsin molecules; (b) the concentration of free ligand for half saturation is 2.0 ± 0.6 μM; (c) the apparent Hill coefficient of the bound versus free ligand relationship is 1.7 ± 0.5; (d) half saturation of the binding sites is sufficient for 85% activation of calcium permeability. A gating mechanism is proposed. Copyright © 1985, Wiley Blackwell. All rights reserve
Meccanismo dell'olfatto: purificazione e caratterizzazione di una proteina della mucosa nasale di bovino
No full text
- …
