Temperature and pH dependence of the metarhodopsin I-metarhodopsin II kinetics and equilibria in bovine rod disk membrane suspensions

• Published in: Biochemistry (Easton) Vol. 23; no. 21; pp. 5054 - 5061
• Main Authors: Parkes, John H, Liebman, Paul A
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 09.10.1984
• Subjects: Animals; Biological and medical sciences; Cattle; Cell Membrane - metabolism; Fundamental and applied biological sciences. Psychology; Hydrogen-Ion Concentration; Kinetics; Mathematics; metarhodopsin I; Models, Biological; Molecular biophysics; Photochemistry. Photosynthesis. Bioluminescence; Photoreceptor Cells - metabolism; Radiation-biomolecule interaction; Retinal Pigments - metabolism; Rhodopsin - analogs & derivatives; Rhodopsin - metabolism; rod outer segment membranes; temperature; Thermodynamics; Disk membrane; Temperature; Photoisomerization; Retina; Suspension; Vertebrata; Mammalia; Thermodynamic parameter; Vision; PH; Artiodactyla; Beef; Kinetics; Ungulata; Photochemistry
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi00316a035

The kinetics of the relaxation of bleached bovine rod disk membrane suspensions from metarhodopsin I into the equilibrium between metarhodopsins I and II were determined at pHs between 5.9 and 8.1 and at temperatures between -1 and 15 degrees C. From these data, thermodynamic equations were generated by two-way linear regression that simultaneously describe the functional dependence on pH and temperature of the pseudo-first-order and true forward rate constants, the reverse and observed rate constants, and the equilibrium constant. Using these equations, we obtained the thermodynamic parameters and the apparent net proton uptake for the transitions from metarhodopsin I to metarhodopsin II and from metarhodopsin I to the activated intermediate. The reversibility of this equilibrium and the effect of aging of the preparation on the measured rate constants were investigated.