title: Assays for activation of opsin by all-trans-retinal.
abstract: The data collected with the techniques discussed in this chapter suggest significant differences between the active conformation(s) of the opsin/atr complex, which are reversibly formed in the dark, and the active conformation (R*) of the meta-II photoproduct. First, there is good evidence for noncovalent opsin/atr complexes with considerable activity (although covalent binding of atr is found in mutant opsins. Even more intriguing, all-trans-retinal in an amount that saturates the activity of the opsin/atr complex toward Gt does not measurably inhibit the access of 11-cis-retinal to the light-sensitive binding site during regeneration (Fig. 2C). On the other hand, forced protonation at or near Glu-134 appears to be an integral mechanism for both the meta-II and the opsin-like activities (Fig. 4). Thus, it is not inconceivable that these two activities of the receptor arise from two fundamentally different conformations, one meta-II-like and one opsin-like. They would be similar with respect to the Gt (or RK) protein-protein interaction but different in their mode of retinal-protein interaction.
authors.affiliation: Institut für Medizinische Physik und Biophysik, Universitätsklinikum Charité, Humboldt Universität zu Berlin, Germany.
authors.forename: K
authors.initials: K
authors.lastname: Sachs
authors.forename: D
authors.initials: D
authors.lastname: Maretzki
authors.forename: K P
authors.initials: KP
authors.lastname: Hofmann
mesh_terms: D000818:Animals; D019393:Arrestin / Q000302:isolation & purification / Q000378:metabolism; D002417:Cattle; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism; D005136:Eye Proteins; D051606:G-Protein-Coupled Receptor Kinase 1; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D010766:Phosphorylation; D011494:Protein Kinases / Q000302:isolation & purification / Q000378:metabolism; D012160:Retina / Q000378:metabolism; D012172:Retinaldehyde / Q000378:metabolism*; D012243:Rhodopsin / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D012374:Rod Cell Outer Segment / Q000737:chemistry / Q000378:metabolism; D017299:Rod Opsins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D013053:Spectrophotometry / Q000379:methods; D015293:Transducin / Q000302:isolation & purification / Q000378:metabolism
chemical_list: D019393:Arrestin; D005136:Eye Proteins; D017299:Rod Opsins; D012243:Rhodopsin; D011494:Protein Kinases; D051606:G-Protein-Coupled Receptor Kinase 1; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D015293:Transducin; D012172:Retinaldehyde