LIGHT-INDUCED PROTEIN CONFORMATIONAL-CHANGES IN THE PHOTOLYSIS OF OCTOPUS RHODOPSIN

Light-induced protein conformational changes in the photolysis of octo pus rhodopsin were measured with a highly sensitive time-resolved tran sient UV absorption spectrophotometer with nanosecond time resolution, A negative band around 280 nm in the lumirhodopsin minus rhodopsin sp ectra suggests that alteration of the environment of some of the trypt ophan residues has taken place before the formation of lumirhodopsin. A small recovery of the absorbance at 280 nm was observed in the trans formation of lumirhodopsin to mesorhodopsin. Kinetic parameters sugges t that major conformational changes have taken place in the transforma tion of mesorhodopsin to acid metarhodopsin. In this transformation, d rastic changes of amplitude and a shift of a difference absorption ban d around 280 nm take place, which suggest that some of the tryptophan residues of rhodopsin become exposed to a hydrophilic environment.