Molecular dynamics of rhodopsin and free opsin: computer simulation

Computer simulation was used to perform a comparative study of the molecular dynamics of rhodopsin containing the chromophore group (11-cis-retinal) and free opsin. The molecular dynamics were followed over a time interval of 3000 psec; a total of 3 x 10(6) discrete conformational states of rhodopsin and opsin. The presence of the chromophore group in the chromophore center of opsin was shown to have significant effects on the immediate protein environment of the chromophore and the conformational state of the cytoplasmic domain, but to have virtually no effect on the conformational state of the intradisk domain. The simulation results are used to discuss the possible intramolecular mechanism by which rhodopsin is maintained as a G-protein-coupled receptor in the inactive state, i.e., the function of the chromophore as an effective antagonist ligand.

Characteristics of the photoconversion of rhodopsin in the early stages of photolysis

Low-temperature spectrophotometry was used to study the primary stages of rhodopsin photolysis. A digitonin extract of rhodopsin was irradiated at -155 degrees C with blue light of wavelength 436 nm. The stage of the bathorhodopsin --> lumirhodopsin conversion was accompanied by the simultaneous formation of several products. Formation of an intermediate product spectrally similar to the known "blue-shifted intermediate" (BSI) was demonstrated. It is suggested that the appearance of more than one intermediate product at each stage of photolysis reflects the existence of several conformational states of the rhodopsin molecule during its photoconversion.

[Participation of cyclic nucleotides and calcium in regulation of the sensitivity of vertebrate photoreceptors]

Effects of PDE inhibitor IBMX and of Ca2+ decrease upon sensitivity of rods and cones were compared. IBMX greatly increases the sensitivity of rods but not that of cones. Ca2+ does not significantly affect the sensitivity of both rods and cones. Possible role of cyclic nucleotides as feed--back regulator in mechanisms of photoreception is discussed.