title: High expression levels in cones of RGS9, the predominant GTPase accelerating protein of rods.
abstract: RGS9 is a member of the RGS family of GTPase accelerating proteins (GAPs) for heterotrimeric G proteins. We have explored its contribution to GTPase acceleration in mammalian rod and cone photoreceptors. When RGS9 was specifically removed from detergent extracts of rod outer segments by immunodepletion, the extracts lost nearly all of their GAP activity stimulatable by the inhibitory subunit of cGMP phosphodiesterase. Immunolocalization using monoclonal antibodies and confocal microscopy revealed that RGS9 is present in cones at significantly higher levels than in rods. Thus, RGS9 is the predominant source of GAP activity in rod outer segments, and RGS9 concentration emerges as a potentially important determinant of the faster response kinetics and lower sensitivity of mammalian cones, as compared with rods.
authors.affiliation: Verna and Marrs McLean Department of Biochemistry and Cell and Molecular Biology Graduate Program, Baylor College of Medicine, Houston, TX 77030, USA.
authors.forename: C W
authors.initials: CW
authors.lastname: Cowan
authors.forename: R N
authors.initials: RN
authors.lastname: Fariss
authors.forename: I
authors.initials: I
authors.lastname: Sokal
authors.forename: K
authors.initials: K
authors.lastname: Palczewski
authors.forename: T G
authors.initials: TG
authors.lastname: Wensel
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002417:Cattle; D019084:Fluorescent Antibody Technique, Indirect; D020558:GTP Phosphohydrolases / Q000378:metabolism; D020690:GTPase-Activating Proteins; D008565:Membrane Proteins / Q000378:metabolism; D011506:Proteins / Q000378:metabolism*; D017949:Retinal Cone Photoreceptor Cells / Q000378:metabolism*; D012374:Rod Cell Outer Segment / Q000378:metabolism; D014785:Vision, Ocular
chemical_list: D020690:GTPase-Activating Proteins; D008565:Membrane Proteins; D011506:Proteins; D020558:GTP Phosphohydrolases