Reduced Light-dependent Phosphorylation of an Analog Visual Pigment Containing 9-Demethylretinal as Its Chromophore

• Published in: The Journal of biological chemistry Vol. 270; no. 12; pp. 6718 - 6721
• Main Authors: Morrison, D F, Ting, T D, Vallury, V, Ho, Y K, Crouch, R K, Corson, D W, Mangini, N J, Pepperberg, D R
• Format: Journal Article
• Language: English
• Published: United States American Society for Biochemistry and Molecular Biology 24.03.1995
• Subjects: Animals; Cattle; Light; Phosphorylation; Retinaldehyde - metabolism; Rhodopsin - analogs & derivatives; Rhodopsin - metabolism; Rod Cell Outer Segment - metabolism
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.270.12.6718

9-Demethyl rhodopsin (9dR), an analog of vertebrate rhodopsin, consists of opsin and a covalently attached chromophore of 11- cis 9-demethylretinal. Electrophysiological evidence that photoactivated 9dR (9dR*) undergoes abnormally slow deactivation in salamander rods (Corson, D. W., Cornwall, M. C., and Pepperberg, D. R.(1994) Visual Neurosci. 11, 91-98) raises the possibility that opsin phosphorylation, a reaction involved in visual pigment deactivation, operates abnormally on 9dR*. This possibility was tested by measuring the light-dependent phosphorylation of 9dR in preparations obtained from bovine rod outer segments. Outer segment membranes containing 9dR or regenerated rhodopsin were flash-illuminated in the presence of [ - P]ATP and rhodopsin kinase, further incubated in darkness, and then analyzed for opsin-bound [ P]P i . [ P]P i incorporation by 9dR* increased with both incubation period and bleaching extent but, under all conditions tested, was less than that measured in rhodopsin controls. Results obtained with 30-s incubation periods indicated that the maximal initial rate of incorporation by 9dR* is about 25% of that by photoactivated rhodopsin. The results imply that the low incorporation of P i by 9dR* results from a reduced rate of phosphorylation by rhodopsin kinase and are consistent with the prolonged lifetime of 9dR* determined electrophysiologically.