Possible Involvement of Retinylidene Phospholipid in Photoisomerization of All-trans-Retinal to 11-cis-Retinal
Year: 1974
Type: article
Abstract: Rhodopsin regeneration from opsin and all-trans-retinal involves two discrete reactions: isomerization of all-trans-retinal to 11-cis-retinal and binding of 11-cis-retinal with opsin. We have previously found that phospholipid stimulates the photic regeneration of rhodopsin. We now report that, if opsin maintains its native conformation after the photic bleaching of the chromophore, phospholipid is not required for retinal binding but is essential for the isomerization reaction. Evidence for the involvement of phospholipid includes: (a) bleached rod outer segments form a complex (λmax = 458 nm) with all-trans-retinal in the dark and convert all-trans-retinal to the 11-cis isomer in the light; (b) 450- to 460-nm light is the most effective for isomerization; (c) the isomerizing activity of partially delipidated rod outer segments is restored by added phosphatidylethanolamine (phosphatidylcholine is without effect and phosphatidylserine is inhibitory); (d) phosphatidylethanolamine can form a complex with all-trans-retinal and is active in the isomerization reaction; and (e) treatment of rod outer segments with guanidine hydrochloride or trichloroacetic acid, extreme pH values (1 and 13), or heat completely denatures opsin protein but affects isomerizing activity only slightly. From these results, we conclude that the isomerizing activity of rod outer segments is not of enzymic nature but can be accounted for by formation of a protonated Schiff base between phosphatidylethanolamine and all-trans-retinal. Kinetic data suggest that about 30 % of the phosphatidylethanolamine molecules associated with rod outer segments are involved in complex formation with all-trans-retinal and retinal remains in the complex after photoisomerization.
Source: Journal of Biological Chemistry
Authors: Hitoshi Shichi, Robert L. Somers
Institutions: National Institutes of Health, National Eye Institute
Language: English
Subfield: Cellular and Molecular Neuroscience
Field: Neuroscience
Domain: Life Sciences
Open Access status: hybrid
Estimated APC paid: $3,430
OpenAlex ID: W1625165810