Difference Spectra Of Late Intermediates Of The Bacteriorhodopsin Photocycle

R. Govindjee; Zs. Dancshazy; T. G. Ebrey

doi:10.1117/12.951655

8 May 1989 Difference Spectra Of Late Intermediates Of The Bacteriorhodopsin Photocycle

R. Govindjee, Zs. Dancshazy, T. G. Ebrey

Proceedings Volume 1057, Biomolecular Spectroscopy; (1989) https://doi.org/10.1117/12.951655
Event: OE/LASE '89, 1989, Los Angeles, CA, United States

Abstract

The flash-induced difference absorbance spectra of bacteriorhodopsin (BR) were measured at various times after an actinic flash using a diode array spectrophotometer (300-700 nm). Difference spectra for three late bacteriorhodopsin photocycle intermediates Mfast (Mf), mslow (Ms) and R are reported. The main distinguishing features of the 3 difference spectra at pH = 10.5 and 5 °C are as follows: Mf ΔAmax = 412 nm, a shoulder at 436 nm, no absorbance change at 350 nm, ΔAmin = 565 nm, ΔA412/ ΔA565 = 0.8-0.9. Ms: ΔAmax = 412 nm, a shoulder at 386 nm, ΔAmin = 570-575 nm, ΔA.412/ ΔA575 = 0.6. R: ΔAmax = 336 and 350 nm (double peak), minor peaks at 386 and 412 nms,ΔAmin = 585-590 nm; ΔA350/ ΔA585 = 0.2. The t1/2 of Mf, Ms and R and the relative weights of BR570 recovered with these rates are: 1 sec (50%), 3-5 sec (25%) and 35 sec (25%) respectively. These spectral features can also be seen at pH = 7, -16 °C, and at pH = 9-10.5, 20 °C. Based on some assumptions, the absorption maximum of R was calculated to be at ca. 550 nm. The extinction coefficient of R is approximately 70% that of light-adapted BR. We suggest that: 1) Mf decays into R and R decays to BR, and 2) there are two types of BR with independent photocycles; Ms and probably 0 are in the photocycle near neutral pH, and Mf and R in a photocycle predominant at higher pH.

Citation Download Citation

R. Govindjee, Zs. Dancshazy, and T. G. Ebrey "Difference Spectra Of Late Intermediates Of The Bacteriorhodopsin Photocycle", Proc. SPIE 1057, Biomolecular Spectroscopy, (8 May 1989); https://doi.org/10.1117/12.951655

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