Functional properties of cattle rhodopsin in soluble complex with phospholipids and deoxycholate.

Abstract

Abstract— The necessary conditions of bleached rhodopsin to activate GTPase and to regenerate α‐band were studied by changing the number of bound phospholipids to rhodopsin using gel filtration procedure. The number of bound phospholipids per mole of rhodopsin (bPL/rho) in the eluants was reproducibly controlled by the concentration of sodium deoxycholate (DOC) in the elution buffer. The eluants were soluble complexes composed of rhodopsin with original a‐band, disk phospholipids and DOC. The regenerability of α‐band depended on bPL/rho but neither on the concentration of DOC nor on state of aggregation of rhodopsin. The lowest number of bPL/rho for this activity under our experimental conditions was estimated to be30–50 in bPL/rho. GTPase was activated only by such complexes that had a nearly original quantity of bPL/rho in disk membranes. Other complexes with less bPL/rho showed aggregation upon bleaching and did not activate GTPase. The amount of phospholipids present in the disk membranes is sufficient to prevent aggregation of rhodopsin upon bleaching.