Recoverin inhibits the phosphorylation of dark-adapted rhodopsin more than it does that of bleached rhodopsin: a possible mechanism through which rhodopsin kinase is prevented from participation in a side reaction.
In its resting state rhodopsin kinase is present in an inactive from and is activated after interaction with light-activated rhodopsin (Rho*). The activated rhodopsin kinase then phosphorylates Rho* but is also able to catalyse the phosphorylation of dark-adapted rhodopsin. A consequence of the latter behaviour of the activated kinase is that at low levels of bleach a large number of phosphoryl groups are incorporated per mol of Rho*. Recoverin- and Ca2+-dependent inhibition of rhodopsin kinase was found to be inversely related to the extent of bleaching; the lower the fraction of rhodopsin bleached, the greater the inhibition. The IC50 of recoverin is approx. 1 microM at a 0.2% level of bleach and about 5 microM in a fully bleached sample. The inhibitory effect of recoverin was studied separately on the phosphorylation of rhodopsin and Rho*. The formation of phosphorylated rhodopsin was inhibited 4.5-fold more strongly than that of phosphorylated Rho*. These results are interpreted to suggest that one of the roles of the recoverin-dependent regulation of the activity of rhodopsin kinase is to prevent the enzyme from participating in the unwanted phosphorylation of dark-adapted rhodopsin, directing it to fulfil its 'correct' function of quenching the transduction activity of Rho*.
Senin
I I
II
Department of Enzymology, A. N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Russia.
Dean
K R
KR
Zargarov
A A
AA
Akhtar
M
M
Philippov
P P
PP
D002118:Calcium / Q000494:pharmacology; D002135:Calcium-Binding Proteins / Q000494:pharmacology*; D003624:Darkness; D005136:Eye Proteins; D051606:G-Protein-Coupled Receptor Kinase 1; D051597:Hippocalcin; D008027:Light; D008074:Lipoproteins; D009419:Nerve Tissue Proteins; D010766:Phosphorylation / Q000187:drug effects; D047428:Protein Kinase Inhibitors; D011494:Protein Kinases / Q000378:metabolism; D051603:Recoverin; D012243:Rhodopsin / Q000378:metabolism* / Q000502:physiology; D012374:Rod Cell Outer Segment / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D014508:Urea
D002135:Calcium-Binding Proteins; D005136:Eye Proteins; D008074:Lipoproteins; D009419:Nerve Tissue Proteins; D047428:Protein Kinase Inhibitors; D051603:Recoverin; D051597:Hippocalcin; D014508:Urea; D012243:Rhodopsin; D011494:Protein Kinases; D051606:G-Protein-Coupled Receptor Kinase 1; D002118:Calcium