Mechanism of retinal schiff base formation and hydrolysis in relation to visual pigment photolysis and regeneration: resonance raman spectroscopy of a tetrahedral carbinolamine intermediate and oxygen-18 labeling of retinal at the metarhodopsin stage in photoreceptor membranes
The mechanism of formation and hydrolysis of N-retinylidene-n-butylamine, as a model of the rhodopsin chromophore, has been investigated by a study of the kinetic and equilibrium properties in aqueous anionic, cationic, and neutral detergent micelle systems. The pH dependence of steady-state formation and hydrolysis rate constants is consistent with the classical imine reaction mechanism involving tetrahedral carbinolamine intermediates. Kinetic transients consistent with such intermediates can be seen using rapid stopped-flow techniques. Hydrolysis rates in neutral detergent micelles exhibit general base catalysis, and there are pronounced detergent-specific effects which can be qualitatively interpreted in terms of ionic effects on Schiff base pK/sub a/ and micellar hydrogen ion activities. This suggests a rational explanation for the anomalous pK/sub a/ and thermodynamic stability of visual pigment chromophores under physiological conditions. The tetrahedral intermediate has been observed directly at room temperature by continuous-flow, pH-jump resonance Raman spectroscopy, and the spectrum of this transient species shows remarkable similarity with the previously reported Raman spectrum of the metarhodopsin II intermediate of bovine rhodopsin photolysis. Isotope-labeling experiments on bovine photoreceptor membranes exposed to oxygen-18 enriched water during bleaching show incorporation of /sup 18/O at the retinal aldehyde site during the metarhodopsin I ..-->.. II transition.
- Research Organization:
- Glasgow Univ., Scotland
- OSTI ID:
- 5527145
- Journal Information:
- J. Am. Chem. Soc.; (United States), Vol. 109:24
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
14 SOLAR ENERGY
AMINES
HYDROLYSIS
PHOTOLYSIS
THERMODYNAMIC PROPERTIES
RHODOPSIN
SIMULATION
CHEMICAL REACTION KINETICS
EQUILIBRIUM
EXPERIMENTAL DATA
LABELLING
MEMBRANES
MICELLAR SYSTEMS
OXYGEN 18
PH VALUE
REACTION INTERMEDIATES
SCHIFF BASES
CHEMICAL REACTIONS
DATA
DECOMPOSITION
EVEN-EVEN NUCLEI
IMINES
INFORMATION
ISOTOPES
KINETICS
LIGHT NUCLEI
LYSIS
NUCLEI
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
OXYGEN ISOTOPES
PHOTOCHEMICAL REACTIONS
PHYSICAL PROPERTIES
PIGMENTS
PROTEINS
REACTION KINETICS
SOLVOLYSIS
STABLE ISOTOPES
400500* - Photochemistry
140505 - Solar Energy Conversion- Photochemical
Photobiological
& Thermochemical Conversion- (1980-)