title: The bilayer enhances rhodopsin kinetic stability in bovine rod outer segment disk membranes.
abstract: Rhodopsin is a kinetically stable protein constituting >90% of rod outer segment disk membrane protein. To investigate the bilayer contribution to rhodopsin kinetic stability, disk membranes were systematically disrupted by octyl-β-D-glucopyranoside. Rhodopsin kinetic stability was examined under subsolubilizing (rhodopsin in a bilayer environment perturbed by octyl-β-D-glucopyranoside) and under fully solubilizing conditions (rhodopsin in a micelle with cosolubilized phospholipids). As determined by DSC, rhodopsin exhibited a scan-rate-dependent irreversible endothermic transition at all stages of solubilization. The transition temperature (T(m)) decreased in the subsolubilizing stage. However, once the rhodopsin was in a micelle environment there was little change of the T(m) as the phospholipid/rhodopsin ratio in the mixed micelles decreased during the fully solubilized stage. Rhodopsin thermal denaturation is consistent with the two-state irreversible model at all stages of solubilization. The activation energy of denaturation (E(act)) was calculated from the scan rate dependence of the T(m) and from the rate of rhodopsin thermal bleaching at all stages of solubilization. The E(act) as determined by both techniques decreased in the subsolubilizing stage, but remained constant once fully solubilized. These results indicate the bilayer structure increases the E(act) to rhodopsin denaturation.
authors.affiliation: Department of Molecular and Cell Biology, University of Connecticut, Storrs, Connecticut, USA.
authors.forename: Scott C
authors.initials: SC
authors.lastname: Corley
authors.forename: Peter
authors.initials: P
authors.lastname: Sprangers
authors.forename: Arlene D
authors.initials: AD
authors.lastname: Albert
mesh_terms: D000042:Absorption / Q000187:drug effects; D000818:Animals; D002152:Calorimetry, Differential Scanning; D002417:Cattle; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D004795:Enzyme Stability / Q000187:drug effects; D005960:Glucosides / Q000494:pharmacology; D007700:Kinetics; D008051:Lipid Bilayers / Q000378:metabolism*; D009995:Osmosis / Q000187:drug effects; D011489:Protein Denaturation / Q000187:drug effects; D012243:Rhodopsin / Q000378:metabolism*; D012374:Rod Cell Outer Segment / Q000187:drug effects / Q000378:metabolism*; D012995:Solubility / Q000187:drug effects; D013997:Time Factors; D044366:Transition Temperature / Q000187:drug effects
chemical_list: D005960:Glucosides; D008051:Lipid Bilayers; C018619:octyl-beta-D-glucoside; D012243:Rhodopsin