Identical Hydrogen-Bonding Strength of the Retinal Schiff Base between Primate Green- and Red-Sensitive Pigments: New Insight into Color Tuning Mechanism.
Three aspects are generally considered in the color-tuning mechanism of vision: (I) chromophore distortion, (II) electrostatic interaction between the protonated Schiff base and counterion, and (III) polarity around the β-ionone ring and polyene chain. Primate green- and red-sensitive proteins are highly homologous but display maximum absorption at 530 and 560 nm, respectively. In the present study, the N-D stretching frequency of monkey green-sensitive protein was identified by using C15-D retinal. The hydrogen-bonding strength between monkey green and red was identical. Together with a previous resonance Raman study, we conclude that the 30 nm difference originates exclusively from the polarity around the β-ionone ring and polyene chain. Three amino acids (Ala, Phe, and Ala in monkey green and Ser, Tyr, and Thr in monkey red, respectively) may be responsible for color tuning together with protein-bound water molecules around the β-ionone ring and polyene chain but not at the Schiff base region.
†Department of Frontier Materials and Sciences, Nagoya Institute of Technology, Showa-ku, Nagoya 466-8555, Japan.
Kota
K
Katayama
‡Department of Organic Chemistry for Life Science, Kobe Pharmaceutical University, Higashinada-ku, Kobe 658-8558, Japan.
Takashi
T
Okitsu
§Primate Research Institute, Kyoto University, Inuyama 484-8506, Japan.
Hiroo
H
Imai
‡Department of Organic Chemistry for Life Science, Kobe Pharmaceutical University, Higashinada-ku, Kobe 658-8558, Japan.
Akimori
A
Wada
†Department of Frontier Materials and Sciences, Nagoya Institute of Technology, Showa-ku, Nagoya 466-8555, Japan.
Hideki
H
Kandori
D000818:Animals; D003118:Color Perception; D006860:Hydrogen Bonding; D045792:Norisoprenoids / Q000737:chemistry; D011090:Polyenes / Q000737:chemistry; D011323:Primates; D012160:Retina / Q000737:chemistry*; D012168:Retinal Pigments / Q000737:chemistry*; D012545:Schiff Bases / Q000737:chemistry; D014867:Water / Q000737:chemistry
D045792:Norisoprenoids; D011090:Polyenes; D012168:Retinal Pigments; D012545:Schiff Bases; D014867:Water; C008157:beta-ionone
color visual pigment; electrostatic interaction; isotope shift; protein-bound water molecule; protonated Schiff base; spectral tuning