X₅. Flash Photolysis of Visual Pigments

The flash illumination of the visual chromophore, retinene produces a long lived excited state (λ max = 4400 Å, t1/2 ∼ 10 −5 seconds) tentatively identified as a triplet. Vitamin A as well as the protonated p‐toluidine complex of retinene show no evidence of a similar long lived state. The implication of these facts relative to the primary photochemical process in vision is discussed. Solutions of cattle rhodopsin when flash illuminated near room temperature produce metarhodopsin as the first detectable photo product. The thermal decay of this intermediate (occuring in three stages) was studied at several temperatures. The rate data indicate that major reversible configurational changes (reversible denaturation) in the protein structure accompany the bleaching of metarhodopsin.