Purpose. The visual pigments, P467 and P521, present in the retina of nocturnal gecko have sequence homology to rhodopsin and human long-wavelength green cone pigments respectively. UV-VIS spectroscopy studies were performed in order to understand the pH-dependent properties of P521 pigment. Results. Two distinct pH-dependent properties of gecko P521 were revealed in our .studies: firstly, the pKa of the Schiff base in 50 mM KC1 is 9.3. As salt concentration increases, the pKa of the Schiff base increases indicating a positively charged membrane environment. The pKa shift is attenuated but still present in detergentsolublized samples. Secondly, a blue-shifted species was observed when the pH is lowered below 3.5. This pH effect is chloride-independent and is not affected by amidation of surface carboxyl groups. Since the blue-shift is reversible, it might be caused by the protonation of one or more residues close to the Schiff base instead of by just acid denaturation. Further investigation of P521 by chemical modification and mutagenesis, focused toward elucidating the mechanisms of these phenomena is ongoing.
|Original language||English (US)|
|Journal||Investigative Ophthalmology and Visual Science|
|State||Published - Dec 1 1997|