Modulation of opsin apoprotein activity by retinal. Dark activity of rhodopsin formed at low temperature.
The bovine opsin apoprotein activates transducin, although at a much reduced level than light-activated rhodopsin (Surya, A., Foster, K., and Knox, B. (1995) J. Biol. Chem. 270, 5024-5031). The ability of retinal to modulate opsin apoprotein activity was investigated using a guanyl nucleotide exchange assay on transducin. 11-cis-Retinal reacted with opsin at 22 degrees C to (a) reform pigment having maximal absorbance at 500 nm and (b) reduce opsin activity by >80%. Pigment formation also occurred at 0 degrees C with a t1/2 of 260 min. However, unlike rhodopsin formed at 22 degrees C (R22), the rhodopsin formed at 0 degrees C (R0) activated transducin with the same half-saturating concentration as opsin in an exhaustive binding assay. Thus, the formation of a protonated Schiff base associated with 500 nm absorbance does not by itself lead to the inactivation of opsin. The R0 conformation was partially inactivated by incubation at 22 degrees C (t1/2 = 61 +/- 9 min), suggesting that it may be an intermediate conformation in the regeneration of rhodopsin.
Surya
A
A
Department of Biochemistry and Molecular Biology, SUNY Health Science Center at Syracuse, Syracuse, New York 13210, USA. arjun_surya-1@sbphrd.com
Knox
B E
BE
D000818:Animals; D002417:Cattle; D003080:Cold Temperature; D003624:Darkness; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D012172:Retinaldehyde / Q000378:metabolism*; D012243:Rhodopsin / Q000378:metabolism*; D012374:Rod Cell Outer Segment / Q000378:metabolism; D017299:Rod Opsins / Q000378:metabolism*; D012545:Schiff Bases / Q000378:metabolism; D015293:Transducin / Q000378:metabolism
D017299:Rod Opsins; D012545:Schiff Bases; D012243:Rhodopsin; D015293:Transducin; D012172:Retinaldehyde