Abstract

Small differences in spectral peak among cone pigments appear to underlie several different human color vision polymorphisms. We recently identified three amino acid substitutions that can account for spectral differences among X-encoded pigments. Each of these appears to produce spectral shifts of specific magnitudes. The one that produces the smallest spectral shift (5–7 nm) is a serine for alanine substitution at amino acid position 180. This substitution may be responsible for cone pigment variations among color normal observers (Science, 252, p. 971). We have tested the hypothesis that this same substitution causes spectral variation in the M pigments of protanopes. Spectral sensitivities of protanopes were measured using ERG flicker photometry. We found two types of protanope (in a sample of seven); one phenotype has an M pigment with a spectral peak of 530 nm and the other has a pigment with a 537-nm peak. The amino acid sequences of the M pigments, deduced from nucleotide sequences of genes from one of each of the two protanope phenotypes, differ at position 180 just as predicted. These results confirm that this substitution produces a 5–7-nm shift in human cone pigments. Several different color vision polymorphisms may be caused by this single substitution.

© 1991 Optical Society of America