Carotenoid and retinoid--two pigments in a gecko eye lens.

The eye lenses of the Moroccan day gecko Quedenfeldtia trachyblepharus contain two different pigments: a retinoid (minor pigment) and a carotenoid (major pigment). The retinoid, all-trans 3, 4-didehydroretinol, is bound to iota-crystallin, which comprises only 2% of the total amount of crystallins. The carotenoid is associated to gammas-crystallin - comprising about 10% of total amount of crystallins--and causes the dark yellow colour of the lens. The absorption spectrum of the isolated carotenoid shows a major, triple-peaked band at 372, 392, and 416 nm and two minor peaks at 284 and 294 nm. This spectrum reminds of that of galloxanthin, a carotenoid found in oil droplets of some avian retinae. The absorption spectrum of the carotenoid-gammas-crystallin complex is shifted 6-8 nm bathochromically. In the lens, this complex absorbs ultraviolet and shortwave blue radiation, supposedly improving the optical quality of the dioptric apparatus and protecting the retina against photodamage. Both the retinoid and the carotenoid are present in eye cups. The lenticular carotenoid of Quedenfeldtia is the first example of a carotenoid in the lens of a terrestrial vertebrate with a sufficiently high concentration to be physiologically effective as a UV-filter. Additionally, it is unique in being the first example of a carotenoid associated with gammas-crystallin.