Phototransduction by vertebrate ultraviolet visual pigments: protonation of the retinylidene Schiff base following photobleaching.
The photochemical and subsequent thermal reactions of the mouse short-wavelength visual pigment (MUV) were studied by using cryogenic UV-visible and FTIR difference spectroscopy. Upon illumination at 75 K, MUV forms a batho intermediate (lambda(max) approximately 380 nm). The batho intermediate thermally decays to the lumi intermediate (lambda(max) approximately 440 nm) via a slightly blue-shifted intermediate not observed in other photobleaching pathways, BL (lambda(max) approximately 375 nm), at temperatures greater than 180 K. The lumi intermediate has a significantly red-shifted absorption maximum at 440 nm, suggesting that the retinylidene Schiff base in this intermediate is protonated. The lumi intermediate decays to an even more red-shifted meta I intermediate (lambda(max) approximately 480 nm) which in turn decays to meta II (lambda(max) approximately 380 nm) at 248 K and above. Differential FTIR analysis of the 1100-1500 cm(-1) region reveals an integral absorptivity that is more than 3 times smaller than observed in rhodopsin and VCOP. These results are consistent with an unprotonated Schiff base chromophore. We conclude that the MUV-visual pigment possesses an unprotonated retinylidene Schiff base in the dark state, and undergoes a protonation event during the photobleaching cascade.
Dukkipati
Abhiram
A
Departments of Chemistry and Biology, Syracuse University, 111 College Place, Syracuse, NY 13244-4100, USA.
Kusnetzow
Anakarin
A
Babu
Kunnel R
KR
Ramos
Lavoisier
L
Singh
Deepak
D
Knox
Barry E
BE
Birge
Robert R
RR
D000818:Animals; D019556:COS Cells; D002417:Cattle; D002851:Chromatography, High Pressure Liquid; D010777:Photochemistry; D011522:Protons; D012168:Retinal Pigments / Q000737:chemistry*; D012176:Retinoids / Q000737:chemistry*
D011522:Protons; D012168:Retinal Pigments; D012176:Retinoids; C121835:retinylidene chromophore