Visual-Pigment Spectra: Implications of the Protonation of the Retinal Schiff Base

Barry Honig, Allen D. Greenberg, Uri Dinur, Thomas G. Ebrey

Research output: Contribution to journalArticlepeer-review

213 Scopus citations


Various models of visual-pigment spectra are critically discussed in terms of the spectral properties of protonated Schiff bases and the common structural features of most proteins. The opsin apoprotein is capable of regulating visual pigment wavelengths in ways that are difficult or impossible to reproduce in model systems. Theories based on solvent effects of the spectra of protonated Schiff bases may be misleading. Careful parameterization using known polyene spectra allows accurate calculation of the spectral properties of protonated Schiff bases. It is shown that an isolated protonated Schiff base of retinal should absorb near 600 nm andthat blue-shifted spectra seen in solution arise from associated counterions or solvent molecules. We conclude that the most plausible specific model of chromophore-protein interactions is one in which the protonated Schiff base is closely associated with its counterion and where additional negatively charged or polar groups are positioned by the protein in the vicinity of the ring half of the chromophore. Pigment absorption maxima, bandwidths, and the A2-A1 pigment absorption differences arise naturally fromthese simple models of pigment spectra.

Original languageEnglish
Pages (from-to)4593-4599
Number of pages7
Issue number21
StatePublished - 1 Oct 1976
Externally publishedYes

ASJC Scopus subject areas

  • Biochemistry


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