Picosecond absorption studies on rhodopsin and isorhodopsin in detergent and native membrane

Picosecond transient absorption spectra of rhodopsin and isorhodopsin were measured at room temperature with a double-beam laser spectrophotometer after excitation at 355 nm. Photolysis studies were performed on rhodopsin solubilized in two different detergents (digitonin and 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate). The resulting rhodopsin/bathorhodopsin absorption difference spectra were measured at times from 35 ps to 250 ns following photoexcitation. Rhodopsin and isorhodopsin in native disk membrane were studied after suspension in 75% glycerol. Isorhodopsin was prepared by photoisomerizing rhodopsin in disk membrane at 77 K. Transient spectra obtained from the visual pigments in native membrane were of a quality approaching that obtained from detergent-solubilized rhodopsin. The batho intermediate derived from isorhodopsin was spectrally the same as that generated by rhodopsin photolysis and was produced with a quantum yield higher than had been predicted on the basis of other studies.