Effects of lipid environment on the light-induced conformational changes of rhodopsin. 1. Absence of metarhodopsin II production in dimyristoylphosphatidylcholine recombinant membranes

Photolysis of bovine rhodopsin in dimyristoylphosphatidylcholine recombinant membranes results in the production of a relatively stable metarhodopsin I like photointermediate that decays slowly to a species with a broad absorbance maximum centered at about 380 nm [O'Brien, D. F., Costa, L. F., & Ott, R. A. (1977) Biochemistry 16, 1295-1303]. On the basis of the results of a variety of chemical and spectroscopic tests, we show that this process corresponds to the production of free retinal plus opsin and not to the slow production of metarhodopsin II. Electron spin resonance studies using a novel disulfide spin-label that is covalently linked to rhodopsin indicate that the apparent arrest of the protein at the metarhodopsin I stage is not due to simple aggregation of the protein in this short-chain, saturated lipid bilayer but must be understood in terms of the effect of the lipid host on the conformational energies of individual protein molecules. Limited production of metarhodopsin II is observed under acidic conditions. Thus, the rhodopsin-dimyristoylphosphatidylcholine recombinants offer a unique system for the study of the effect of the phospholipid bilayer environment on the conformation of an intrinsic membrane protein.