Evidence for the specific interaction of a lipid molecule with rhodopsin which is altered in the transition to the active state metarhodopsin II

Comparing the FTIR difference spectra of the rhodopsin --> metarhodopsin II transition in membranes and in dadecylmaltoside detergent, characteristic variations are observed between 1715 and 1750 cm(-1), By repeating the measurements with the rhodopsin mutant D83N/E122Q, the spectral variation between the samples in membranes versus detergent could he assigned to a difference band at 1743(+)/1724(-) cm(-1), which does not exhibit a deuteration-induced downshift. We provide evidence that this band is probably caused by the C=O stretch of only one eater group of one lipid molecule, This group interacts with the dark state of rhodopsin, whereas in metarhodopsin II, the lipid molecule behaves as if it were in the bulb lipid phase. (C) 1998 Federation of European Biochemical Societies.