PHOTOCHEMICAL AND BIOCHEMICAL-PROPERTIES OF CHICKEN BLUE-SENSITIVE CONE VISUAL PIGMENT

Through low-temperature spectroscopy and G-protein (transducin) activa ting experiments, we have investigated molecular properties of chicken blue, the cone visual pigment present in chicken blue-sensitive cones , and compared them with those of the other cone visual pigments, chic ken green and chicken red (iodopsin), and rod visual pigment rhodopsin . Irradiation of chicken blue at -196 degrees C results in formation o f a batho intermediate which then converts to BL, lumi, meta I, meta I I, and meta III intermediates with the transition temperatures of -160 , -110, -40, -20, and -10 degrees C. Batho intermediate exhibits an un ique absorption spectrum having vibrational fine structure, suggesting that the chromophore of bathe intermediate is in a C-6-C-7 conformati on more restricted than those of chicken blue and its isopigment. As r eflected by the difference in maxima of the original pigments, the abs orption maxima of batho, BL, and lumi intermediates of chicken blue ar e located at wavelengths considerably shorter than those of the respec tive intermediates of chicken green, red and rhodopsin, but the maxima of meta I, meta II, and meta III are similar to those of the other vi sual pigments. These facts indicate that during the lumi-to-meta I tra nsition, retinal chromophore changes its original position relative to the amino acid residues which regulate the maxima of original pigment s through electrostatic interactions. Using time-resolved low-temperat ure spectroscopy, the decay rates of meta II and meta III intermediate s of chicken blue are estimated to be similar to those of chicken red and green, but considerably faster than those of rhodopsin. Efficiency in activating transducin by the irradiated chicken blue is greatly di minished as the time before its addition to the reaction mixture conta ining transducin and GTP increases, while that by irradiated rhodopsin is not. The time profile is almost identical with those observed in c hicken red and green. Thus, the faster decay of enzymatically active s tate is common in cone visual pigments, independent of their spectral sensitivity.