Glutamic acid-113 serves as the retinylidene Schiff base counterion in bovine rhodopsin

Proc Natl Acad Sci U S A. 1989 Nov;86(21):8309-13. doi: 10.1073/pnas.86.21.8309.


The characteristic wavelength at which a visual pigment absorbs light is regulated by interactions between protein (opsin) and retinylidene Schiff base chromophore. By using site-directed mutagenesis, charged amino acids in bovine rhodopsin transmembrane helix C were systematically replaced. Substitution of glutamic acid-134 or arginine-135 did not affect spectral properties. However, substitution of glutamic acid-122 by glutamine or by aspartic acid formed pigments that were blue-shifted in light absorption (lambda max = 480 nm and 475 nm, respectively). While the substitution of glutamic acid-113 by aspartic acid gave a slightly red-shifted pigment (lambda max = 505 nm), replacement by glutamine formed a pigment that was strikingly blue-shifted in light absorption (lambda max = 380 nm). The 380-nm species existed in a pH-dependent equilibrium with a 490-nm species such that at acidic pH all of the pigment was converted to lambda max = 490 nm. We conclude that glutamic acid-113 serves as the retinylidene Schiff base counterion in rhodopsin. We believe that this opsin-chromophore interaction is an example of a general mechanism of color regulation in the visual pigments.

Publication types

  • Comparative Study
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Aspartic Acid
  • Cattle
  • GTP Phosphohydrolases / metabolism
  • Glutamates*
  • Glutamic Acid
  • Kinetics
  • Membrane Proteins / metabolism
  • Molecular Sequence Data
  • Mutation
  • Protein Conformation
  • Retinal Pigments / metabolism*
  • Retinoids / metabolism*
  • Rhodopsin / genetics
  • Rhodopsin / metabolism*
  • Schiff Bases
  • Sequence Homology, Nucleic Acid
  • Transducin / metabolism


  • Glutamates
  • Membrane Proteins
  • Retinal Pigments
  • Retinoids
  • Schiff Bases
  • Aspartic Acid
  • Glutamic Acid
  • Rhodopsin
  • GTP Phosphohydrolases
  • Transducin