8 May 1989 Difference Spectra Of Late Intermediates Of The Bacteriorhodopsin Photocycle
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Proceedings Volume 1057, Biomolecular Spectroscopy; (1989) https://doi.org/10.1117/12.951655
Event: OE/LASE '89, 1989, Los Angeles, CA, United States
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.
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R. Govindjee, Zs. Dancshazy, T. G. Ebrey, "Difference Spectra Of Late Intermediates Of The Bacteriorhodopsin Photocycle", Proc. SPIE 1057, Biomolecular Spectroscopy, (8 May 1989); doi: 10.1117/12.951655; https://doi.org/10.1117/12.951655

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