Iodopsin

Literature References: One of 3 visual pigments found in retinal cone cells. Absorption maximum approx 560 nm. Biological activity is similar to that of rhodopsin, q.v. Composed of the chromophore, 11-cis retinal, q.v., bound to photopsin, the specific protein component of cone pigments. (See Opsins). Isoln from chicken retinas: G. Wald, Nature 140, 545 (1937). Prepn from 11-cis retinal and opsin: G. Wald et al., J. Gen. Physiol. 38, 623 (1955). Methods for purification, prepn, and assay: R. Hubbard et al., Methods Enzymol. 18, 615-653 (1971). Exposure to light initiates the conversion of iodopsin through a series of distinct intermediates to yield opsin and trans-retinal. Photochemistry: R. Hubbard, A. Kropf, Nature 183, 448 (1959); T. Yoshizawa, G. Wald, ibid. 214, 566 (1967). Studies on the iodopsin binding site: H. Matsumoto et al., Biochim. Biophys. Acta 404, 300 (1975). Three distinct pigments are responsible for color vision: W. B. Marks et al., Science 143, 1181 (1964); P. K. Brown, G. Wald, ibid. 144, 45 (1964). The variation in the absorption maximum of the 3 pigments is regulated by differences in the apoprotein portion of the molecule: R. Hubbard, L. Sperling, Exp. Eye Res. 17, 581 (1973); B. Honig et al., J. Am. Chem. Soc. 101, 7084 (1979). Reviews: G. Wald, Science 162, 230-239 (1968); H. Matsumoto, T. Yoshizawa, Methods Enzymol. 81, 154-160 (1982). General review of the visual process: P. S. Zurer, Chem. Eng. News 61, 24-35 (Nov. 28, 1983).