title: Illuminated rhodopsin is required for strong activation of retinal guanylate cyclase by guanylate cyclase-activating proteins.
abstract: We have recently shown that activation of retinal guanylate cyclase (retGC) by GC-activating proteins (GCAPs) is much stronger than that previously reported and that preincubation of photoreceptor outer segment homogenates with ATP or its analogue, adenylyl imidodiphosphate (AMP-PNP), is required for the strong activation [Yamazaki, A., Yu, H., Yamazaki, M., Honkawa, H., Matsuura, I., Usukura, J., and Yamazaki, R. K. (2003) J. Biol. Chem. 278, 33150-33160]. Here we show that illuminated rhodopsin is essential for development of the AMP-PNP incubation effect. This was demonstrated by illumination of dark homogenates and treatments of illuminated homogenates with 11-cis-retinal and hydroxylamine prior to the AMP-PNP incubation and by measurement of the GCAP2 concentration required for 50% activation. We also found that the AMP-PNP incubation effect was not altered by addition of guanosine 5'-O-(3-thiotriphosphate), indicating that transducin activation is not required. It is concluded that illuminated rhodopsin is involved in retGC activation in two ways: to initiate the ATP incubation effect for preparation of retGC activation as shown here and to reduce the Ca2+ concentrations through cGMP phosphodiesterase activation as already known. These two signal pathways may be activated in a parallel and perhaps proportional manner and finally converge for strong activation of retGC by Ca2+-free GCAPs.
authors.affiliation: Kresge Eye Institute and Departments of Ophthalmology and Pharmacology, Wayne State University, Detroit, Michigan 48201, USA. ayamazak@med.wayne.edu
authors.forename: Akio
authors.initials: A
authors.lastname: Yamazaki
authors.forename: Matsuyo
authors.initials: M
authors.lastname: Yamazaki
authors.forename: Russell K
authors.initials: RK
authors.lastname: Yamazaki
authors.forename: Jiro
authors.initials: J
authors.lastname: Usukura
mesh_terms: D015106:3',5'-Cyclic-GMP Phosphodiesterases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000378:metabolism; D000266:Adenylyl Imidodiphosphate / Q000378:metabolism; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D004789:Enzyme Activation; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D006162:Guanylate Cyclase / Q000737:chemistry / Q000378:metabolism*; D051604:Guanylate Cyclase-Activating Proteins / Q000737:chemistry / Q000378:metabolism*; D019811:Hydroxylamine / Q000378:metabolism; D008027:Light; D010786:Photoreceptor Cells / Q000201:enzymology; D012160:Retina / Q000201:enzymology*; D012172:Retinaldehyde / Q000378:metabolism; D012243:Rhodopsin / Q000737:chemistry / Q000378:metabolism*; D013997:Time Factors; D015293:Transducin / Q000378:metabolism
chemical_list: D051604:Guanylate Cyclase-Activating Proteins; D000266:Adenylyl Imidodiphosphate; D019811:Hydroxylamine; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D000255:Adenosine Triphosphate; D012243:Rhodopsin; D015106:3',5'-Cyclic-GMP Phosphodiesterases; D015293:Transducin; D006162:Guanylate Cyclase; D012172:Retinaldehyde; D002118:Calcium