Reduced light-dependent phosphorylation of an analog visual pigment containing 9-demethylretinal as its chromophore.
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 [gamma-32P]ATP and rhodopsin kinase, further incubated in darkness, and then analyzed for opsin-bound [32P]Pi. [32P]Pi 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 Pi by 9dR* results from a reduced rate of phosphorylation by rhodopsin kinase and are consistent with the prolonged lifetime of 9dR* determined electrophysiologically.
Morrison
D F
DF
Lions of Illinois Eye Research Institute, Department of Ophthalmology and Visual Sciences, University of Illinois, Chicago College of Medicine 60612.
Ting
T D
TD
Vallury
V
V
Ho
Y K
YK
Crouch
R K
RK
Corson
D W
DW
Mangini
N J
NJ
Pepperberg
D R
DR
D000818:Animals; D002417:Cattle; D008027:Light; D010766:Phosphorylation; D012172:Retinaldehyde / Q000378:metabolism*; D012243:Rhodopsin / Q000031:analogs & derivatives / Q000378:metabolism*; D012374:Rod Cell Outer Segment / Q000378:metabolism
D012243:Rhodopsin; D012172:Retinaldehyde