AN ANALYSIS OF 2 SPECTRAL PROPERTIES OF VERTEBRATE VISUAL PIGMENTS

Spectral data are scrutinized on two properties: (1) the chromophore-i nduced wavelength shift, i.e. the variation in absorbance maximum (lam bda(max)) upon exchanging the vitamin A(1)-based chromophore with one based on vitamin A(2) in the same opsin; (2) the half-band width (HBW) variation as a function of the reciprocal of the peak absorbance (lam bda(max))(-1). It is shown that in an extended spectral range that inc ludes the UV and when data are plotted in wavenumbers, the chromophore -induced shifts can be approximated with a parabola, whose minimum occ urs near 23,000 cm(-1) (approximate to 430 nm). Similarly, HBW variati ons can also be fitted with parabolas, however, these show maxima near 430 nm. The theoretical implications of the two phenomena concerning lambda(max) tuning in vertebrate visual pigments are discussed.