Effects of lipid environment on the light-induced conformational changes of rhodopsin. 2. Roles of lipid chain length, unsaturation, and phase state

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Abstract
When rhodopsin is incorporated into the saturated short-chain phospholipid dimyristoylphosphatidylcholine, photolysis of the protein results in an abnormal sequence of spectral transitions, and the dominant product of metarhodopsin I decay is free retinal plus opsin [Baldwin, P.A., and Hubbell, W. L. (1985)]. By incorporation of rhodopsin into a series of phosphatidylcholines of defined composition, the properties of the lipid environment that are responsible for the altered spectral behavior were determined. Metarhodopsin II is not found in appreciable amounts in bilayers containing acyl chains that are too short (.ltoreq. 14 carbon atoms in length), in the presence of only n-alkyl chains, or below the characteristic phase-transition temperature of recombinant membranes. Double bonds are not required for the formation of the metarhodopsin II intermediate, as it is observed in diphytanoylphosphatidylcholine recombinants.