Excitation Spectrum of the N Intermediate in the Photocycle of Bacteriorhodopsin

Abstract

We obtained the absorption spectrum of the N intermediate that plays an important role in the proton uptake during the photocycle of bacteriorhodopsin. The reported spectra of N that were reconstituted from the transient difference absorption spectrum depended on the assumed kinetic models such as sequential M f N f O reaction and M a N a O quasi-equilibrium. In this work we measured the excitation spectrum of N by monitoring the characteristic absorption of Q (a photoproduct of N) at 664 nm. The λ max and max of N were 559 ( 3 nm and (4.30 ( 0.75) × 10 4 M -1 cm -1 , respectively. The present spectrum is consistent with the results of the recent SVD analysis. This work provides independent evidence that Q is photochemically formed from N.

Mechanism of voltage-sensitive fluorescence in a microbial rhodopsin

“…Although the photocycle was initially viewed as a series of sequential steps (13,14), kinetic evidence suggests rapid equilibrium among the states within the 13-cis manifold (15)(16)(17). Excitation of photocycle intermediates generates off-pathway states, some of which have been reported to be fluorescent (18)(19)(20)(21).…”

Photochemistry of a Dual-Bacteriorhodopsin System in Haloarcula marismortui: HmbRI and HmbRII

“…As the pH was adjusted to 5.8 and 7, the contours of the bR recovery at 550 nm and the intermediate O changed. An asymmetric recovery contour, on the short-wavelength side of the depletion band at 550 nm after 1 ms delay, referred to intermediate N, whose absorption contour was slightly blue-shifted with respect to the depletion of HsbR . A simplified mechanism, adapting the conventional reversible kinetics model, ,, was established for analysis of the observed time-resolved difference spectra using global analysis () , HsbR → normalM .25ex2ex → k normalM → normalN , normalO ← k normalN , normalO → normalM normalN , normalO → k normalN , normalO → bR HsbR …”