EFFECT OF FLASH ILLUMINATION ON RHODOPSIN IN SOLUTION

This paper describes some of the results obtained using the flash-photolysis technique' to study the photochemical behavior of rhodopsin in solution, a preliminary report of which appears elsewhere.2 Subjecting a solution of rhodopsin to a short, intense flash of light permits nearly simultaneous excitation of the pigment molecules. Subsequent changes of the pigment molecules can then be studied by means of a fast spectrophotometric technique that permits the measurement of absorption changes only microseconds after illumination. In brief, the results we obtained using this method demonstrate that flash excitation of rhodopsin in solution produces the following: (1) an initial photoproduct having an absorption spectrum different from that of rhodopsin; (2) spontaneous and partial disappearance of this photoproduct (dark reactions) in several well-defined stages; and ( 3 ) a terminal and stable, but light-sensitive, photoproduct. Since visual excitation must be initiated by photochemical events occurring immediately upon or shortly after photoexcitation, it seemed desirable to study the behavior of rhodopsin immediately following flash illumination.