The violet-and ultraviolet-sensitive visual pigments of birds belong to the same class of pigments as the violet-sensitive (so-called blue) pigments of mammals. However, unlike the pigments from mammals and other vertebrate taxa which, depending on species, have #lambda#_max values of either around 430 nm or around 370 nm, avian pigments are found with #lambda#_max values spread across this range. In this paper, we present the sequences of two pigments isolated from Humbolt penguin and pigeon with intermediate #lambda#_max values of 403 and 409 nm, respectively. By comparing the amino acid sequences of these pigments with the true UV pigments of buderigar and canary and with chicken violet with a #lambda#_max value of 420 nm, we have been able to identify five amino acid sites that show a pattern of substitution between species that is consistent with differences in #lambda#_max .Each of these substitutions has been introduced into budgerigar cDNA and expressed in vitro in COS-7 cells. Only three resulted in spectral shifts in the regenerated pigment; two had relataively small effects and may accoun for the spectral shifts between penguin, pigeon, and chicken whereas one, the replacement of Ser by Cys at site 90 in the UV pigments, produced a 35 nm shortwave shift that could account for the spectral shift from 403 nm in penguin to around 370 nm in budgerigar and canary.
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