The DNAs from 217 Japanese males with congenital red/green color-vision deficiencies were analyzed. Twenty-three subjects had the normal genotype of a single red gene, followed by a green gene. Four of the 23 were from the 69 protan subject group and 19 of the 23 were from the 148 deutan subject group. Three of the 23 subjects had missense mutations. The mutation Asn94Lys (AAC --> AAA) occurred in the single green gene of a deutan subject (A155). The Arg330Gln (CGA --> CAA) mutation was detected in both green genes of another deutan subject (A164). The Gly338Glu (GGG --> GAG) mutation occurred in the single red gene of a protan subject (A89). Both normal and mutant opsins were expressed in cultured COS-7 cells and visual pigments were regenerated with 11-cis-retinal. The normal red and green opsins showed absorbance spectra with lambda(max) of 560 and 530 nm, respectively, but the three mutant opsins had altered spectra. The mutations in Asn94Lys and Gly338Glu resulted in no absorbance and the Arg330Gln mutation gave a low absorbance spectrum with lambda(max) of 530 nm. Therefore these three mutant opsins are likely to be affected in the folding process, resulting in a loss of function as a visual pigment. (C) 2002 Elsevier Science (USA). All rights reserved.