Merbs & Nathans photopigment spectra

Data key

Columns

1. Wavelength (nm)
2. L-cone with serine at position 180
3. L-cone with alanine at position 180
4. M-cone
5. S-cone (uncorrected for bleaching products)
6. S-cone (corrected for bleaching products)

Notes

Photobleaching difference absorption spectra of human cone pigments produced in cultured cells.

Data courtesy of Jeremy Nathans.

λ_max values for normal and hybrid red-green pigments

    Estimates of the peaks of the absorption spectra of the pigments manufactured by the normal and hybrid pigment genes have been determined by Merbs & Nathans (1992a,b), who constructed hybrid genes from cDNA clones for the normal red and green photopigments and expressed them in cultured mammalian kidney cells. The gene products -- the artificial opsins -- were then combined with 11-cis-retinal and the cell membranes were solubilized in detergent. The absorption spectra of the resulting pigments were estimated by subtracting the absorption at each wavelength before and after bleaching (i.e., by means of photobleaching difference absorption spectroscopy). The absorption spectra of these recombinant human cone pigments, given in Table 1, indicate that the spectral sensitivity of each hybrid pigment is intermediate between the parental green and red pigment sensitivities. The amount of spectral shift depends upon the exons involved in the cross-over or fusion. Amino acids encoded by exons 2, 3, 4 and 5 produce spectral shifts at the wavelength of maximal absorbance of 0 to 4, 0 to 4, 3 to 4, and 15 to 21 nm, respectively, the exact value depending on the identities of amino acids elsewhere in the hybrid.

References

Merbs, S. L. & Nathans, J. (1992a). Absorption spectra of the hybrid pigments responsible for anomalous color vision. Science, 258, 464-466.

Merbs, S. L. & Nathans, J. (1992b). Photobleaching difference absorption spectra of human cone pigments: quantitative analysis and comparison to other methods. Photochemistry and Photobiology, 56, 869-881.