Pathways of the rise and decay of the M photointermediate(s) of bacteriorhodopsin

Journal Article · Tue Mar 06 00:00:00 EST 1990 · Biochemistry; (USA)

DOI:https://doi.org/10.1021/bi00461a006· OSTI ID:6956401

Varo, G; Lanyi, J K ^[1]

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1. Univ. of California, Irvine (USA)

The photocycle of bacteriorhodopsin (BR) was studied at alkaline pH with a gated multichannel analyzer, in order to understand the origins of kinetic complexities in the rise and decay of the M intermediate. The results indicate that the biphasic rise and decay kinetics are unrelated to a photoreaction of the N intermediate of the BR photocycle, proposed earlier by others. Rather, under conditions where N did not accumulate in appreciable amounts (high pH, low salt concentration), they were accounted for by conventional kinetic schemes. These contained reversible interconversions, either M {leftrightarrow} N in one of two parallel photocycles or L {leftrightarrow} M as well as M {leftrightarrow} N in a single photocycle. Monomeric BR also showed these kinetic complications. Conditions were then created where N accumulated in a photo steady state (high pH, high salt concentration, background illumination). The apparent increase in the proportion of the slow M decay component by the background illumination could be quantitatively accounted for with the single photocycle model, by the mixing of the relaxation of the background light induced photo steady state with the inherent kinetics of the photocycle. Postulating a new M intermediate which is produced by the photoreaction of N was neither necessary nor warranted by the data. The difference spectra suggested instead that absorption of light by N generates only one intermediate, observable between 100 ns and 1 ms, which absorbs near 610 nm. Thus, the photoreaction of N resembles in some respects that of BR containing 13-cis-retinal.

• OSTI ID: 6956401
• Journal Information: Biochemistry; (USA), Vol. 29:9; ISSN 0006-2960
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
PHOTOSYNTHETIC BACTERIA
BIOLOGICAL PATHWAYS
REACTION INTERMEDIATES
ABSORPTION SPECTRA
RHODOPSIN
BIOCHEMICAL REACTION KINETICS
PH VALUE
VITAMIN A
KINETICS
ORGANIC COMPOUNDS
PIGMENTS
PROTEINS
REACTION KINETICS
SPECTRA
VITAMINS
140505* - Solar Energy Conversion- Photochemical
Photobiological
& Thermochemical Conversion- (1980-)