Zinc causes an apparent increase in rhodopsin phosphorylation.
OBJECTIVE
Rhodopsin is a zinc-binding protein. We investigated the effect of low concentrations of zinc on the initial phosphorylation of rhodopsin.


METHODS
Dark-adapted bovine rod outer segments (ROS) were incubated with (gamma 32P) ATP and 5 mM magnesium in the presence and absence of micromolar amounts of zinc. The ROS were exposed to light to initiate phosphorylation under conditions which allow only limited initial phosphorylation.


RESULTS
We found that zinc enhanced the rhodopsin phosphorylation apparent on autoradiographies by several fold. Phosphorylation reactions conducted in the presence of potent phospho-opsin phosphatase inhibitors show a comparable zinc-enhanced phosphorylation of rhodopsin. Under our reaction conditions, ROS membranes also appear more red upon initial exposure to light when zinc is present.


CONCLUSIONS
Zinc can increase initial rhodopsin phosphorylation, apparently acting at the substrate rhodopsin and not at relevant phosphatases or rhodopsin kinase. How zinc binding to rhodopsin might increase its ability to serve as a substrate for phosphorylation is under investigation.
Shuster
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TA
Department of Biological Sciences, California State University, Long Beach 90840-3701, USA.
Martin
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Nagy
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AK
D000818:Animals; D001345:Autoradiography; D001665:Binding Sites; D002417:Cattle; D003623:Dark Adaptation; D004591:Electrophoresis, Polyacrylamide Gel; D005136:Eye Proteins; D051606:G-Protein-Coupled Receptor Kinase 1; D010766:Phosphorylation / Q000187:drug effects; D010770:Phosphotransferases / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism; D012243:Rhodopsin / Q000187:drug effects / Q000378:metabolism*; D012374:Rod Cell Outer Segment / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D013053:Spectrophotometry; D015032:Zinc / Q000494:pharmacology*
D005136:Eye Proteins; D012243:Rhodopsin; D010770:Phosphotransferases; D011494:Protein Kinases; D051606:G-Protein-Coupled Receptor Kinase 1; D015032:Zinc