Metarhodopsin intermediates of the gecko cone pigment P521

Jie Liang, Rajni Govindjee, Thomas G. Ebrey
1993 Biochemistry  
Cone visual pigments are responsible for color vision. Using low-temperature spectroscopy and linear/logarithmic time scale flash photolysis, we studied the photochemistry of the cone visual pigment P521 from the lizard Gekko gekko. We found both meta I and meta I1 intermediates in this cone pigment; meta I absorbs a t 480 nm, and meta I1 absorbs at ca. 380 nm. The formation of meta I is a fast process with a lifetime of 2.8 ps for the slow component (pH 6.70, 8.0 O C , 2% digitonin) compared
more » ... gitonin) compared to 2.1 ps for bovine rhodopsin under these conditions. The formation of meta I1 does not have single-exponential kinetics but can be better characterized by fast and slow components. High p H favors faster kinetics of meta I1 formation, but less is formed. The amount of meta I1 formed has a pKa of 8.7. The fast component of the meta I1 formation seems to have a somewhat lower pK, (e.g., 6.4). Temperature also affects meta I1 formation, with high temperature favoring a faster rate and larger amounts. The higher pKa of the meta I to meta I1 transition in gecko P521 compared to a rod pigment like bovine rhodopsin (pK, = 6.4) probably is due to a cysteine residue a t position 21 1 in gecko rather than a histidine residue in bovine rhodopsin.
doi:10.1021/bi00214a018 pmid:8260505 fatcat:u4zt5kc7cjcdzlxzhtvvzdcqgi