The catalytic subunit of phosphatase 2A dephosphorylates phosphoopsin.
Rod cell outer segments were found to contain a protein phosphatase activity toward phosphoopsin with properties very similar to those of protein phosphatase 1 or 2A. The opsin phosphatase activity was stable to ethanol precipitation, had a Mr of 35,000-38,000 as determined by gel filtration, and was not dependent on divalent cations for activity. The chromatographic properties on DEAE-cellulose of the rod outer segment protein phosphatase were also similar to those reported for protein phosphatase 1 or 2A. In order to distinguish between these two protein phosphatases, we tested homogeneous preparations of protein phosphatases 1 and 2A from skeletal muscle for activity toward phosphoopsin. Protein phosphatase 2A dephosphorylated phosphoopsin at approximately 10% of its rate toward phosphorylase a, whereas protein phosphatase 1 had no activity toward phosphoopsin. We conclude that protein phosphatase 2A is present in the rod cell outer segment and that it is a likely candidate to perform the in vivo dephosphorylation of rhodopsin in the visual cycle.
Palczewski
K
K
Department of Ophthalmology, University of Florida, Gainesville 32610-0284.
Hargrave
P A
PA
McDowell
J H
JH
Ingebritsen
T S
TS
D000818:Animals; D002417:Cattle; D002850:Chromatography, Gel; D002851:Chromatography, High Pressure Liquid; D002852:Chromatography, Ion Exchange; D005136:Eye Proteins / Q000378:metabolism*; D051606:G-Protein-Coupled Receptor Kinase 1; D007700:Kinetics; D046911:Macromolecular Substances; D010749:Phosphoprotein Phosphatases / Q000302:isolation & purification / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism*; D010762:Phosphorylase a / Q000302:isolation & purification / Q000378:metabolism; D010786:Photoreceptor Cells / Q000201:enzymology*; D011494:Protein Kinases / Q000302:isolation & purification / Q000378:metabolism; D054645:Protein Phosphatase 1; D054648:Protein Phosphatase 2; D012374:Rod Cell Outer Segment / Q000201:enzymology*; D017299:Rod Opsins
D005136:Eye Proteins; D046911:Macromolecular Substances; D010750:Phosphoproteins; D017299:Rod Opsins; C059623:phosphoopsin; D010762:Phosphorylase a; D011494:Protein Kinases; D051606:G-Protein-Coupled Receptor Kinase 1; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D054648:Protein Phosphatase 2