Abstract
Photoisomerization of rhodopsin's chromophore, 11-cis-retinaldehyde, and subsequent regeneration of the 11-cis configuration are accomplished in vertebrates by a series of reactions known as the visual cycle. At one point in the cycle, 11-cis-retinol can either be enzymatically oxidized to 11-cis-retinaldehyde and exported for visual pigment regeneration or be enzymatically esterified and stored. Partition of substrate at this branch was examined in this study and found to be influenced by cellular retinaldehyde-binding protein (CRALBP), a retinoid-binding protein found in retina. Esterification was reduced to about 10% and oxidation stimulated 2-3-fold in the presence of this protein. Other experiments confirmed that "free" 11-cis-retinol was esterified more rapidly than 11-cis-retinol complexed with CRALBP and that CRALBP.11-cis-retinol was not an inhibitor of the esterification. Following oxidation of CRALBP.11-cis-retinol, the reaction product, 11-cis-retinaldehyde, was found associated with the binding protein. 11-cis-Retinaldehyde is not available for reaction with carbonyl reagents when the retinoid is bound to CRALBP. However, enzymatic oxidation of CRALBP.11-cis-retinol in the presence of O-ethylhydroxylamine produced ca. 30% retinaldehyde O-ethyloxime and 70% free 11-cis-retinaldehyde, suggesting that about one-third of the retinol oxidized had dissociated from the binding protein. Neither oxidation nor esterification of CRALBP.11-cis-retinol was inhibited by including CRALBP.11-cis-retinaldehyde in the reaction mixture.(ABSTRACT TRUNCATED AT 250 WORDS)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.