MODULATION OF OPSIN APOPROTEIN ACTIVITY BY RETINAL - DARK ACTIVITY OF RHODOPSIN FORMED AT LOW TEMPERATURE

摘要

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 t(1/2) of 260 min, However, unlike rhodopsin formed at 22 degrees C (R-22), th, rhodopsin formed at 0 degrees C (R-0) 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 R-0 conformation was partially inactivated by incubation at 22 degrees C (t(1/2) = 61 +/- 9 min), suggesting that it may be an intermediate conformation in the regeneration of rhodopsin. References: 54