Purification and low temperature spectroscopy of gecko visual pigments green and blue

We purified two kinds of visual pigments, gecko green and gecko blue, from retinas of Tokay geckos (Gekko gekko) by two steps of column chromatography, and investigated their photobleaching processes by means of low temperature spectroscopy. Absorption maxima of gecko green and blue solubilized in a mixture of 3-[(3-cholamidopropyl)dimethylammonio]-1- propanesulfonate (CHAPS) and phosphatidylcholine were 522 and 465 nm, respectively, which are close to those observed in the photoreceptor cells. Low temperature spectroscopy identified six intermediates in the photobleaching process of gecko green; batho (lambda max = 569 nm), BL (lambda max = 519 nm), lumi (507 nm), meta I (approximately 486 nm), meta II (approximately 384 nm), and meta III intermediates (approximately 500 nm). In contrast to the high similarity in amino acid sequence between gecko green and iodopsin [Kojima, D., et al. (1992) Proc. Natl. Acad. Sci. U.S.A. 89, 6841-6845], the batho-green did not revert thermally to original gecko green but converts to the next intermediate. The photobleaching process of gecko blue was investigated by low temperature spectroscopy, and three intermediates, meta I (lambda max = approximately 470 nm), meta II (lambda max = approximately 370 nm) and meta III (lambda max = approximately 475 nm), were identified. A comparative study on the thermal behavior of meta intermediates revealed that the thermal stability of meta II intermediate of both of the gecko visual pigments is lower than that of metarhodopsin II. The result supports the idea that both the gecko visual pigments are cone-type ones.