Spectral tuning in the human blue cone pigment.

The first determination of the absolute absorption maximum of the human blue cone visual pigment is presented. After expression in COS cells, reconstitution with 11-cis-retinal, and purification, the blue pigment exhibits an absolute absorption maximum of 414 nm. The pigment reacts rapidly with hydroxylamine in the dark and is capable of activating bovine rod transducin in a light-dependent manner. Products of mutations of proposed spectral tuning residues in the blue pigment do not behave as predicted when using rhodopsin mutants as a model. Mutations of amino acids in the ring portion of the chromophore binding pocket of rhodopsin serve well as a predictive model for mutations in the blue pigment, but mutations near the Schiff base do not.