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THE EFFECT OF VISCOSITY ON THE PHOTOCYCLE OF BACTERIORHODOPSIN
Author(s) -
Beece D.,
Bowne S. F.,
Czégé J.,
Eisenstein L.,
Frauenfelder H.,
Good D.,
Marden M. C.,
Marque J.,
Ormos P.,
Reinisch L.,
Yue K. T.
Publication year - 1981
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1981.tb05454.x
Subject(s) - viscosity , arrhenius equation , solvent , bacteriorhodopsin , chemistry , kinetics , flash photolysis , halobacteriaceae , thermodynamics , activation energy , analytical chemistry (journal) , reaction rate constant , halobacterium salinarum , organic chemistry , physics , membrane , biochemistry , quantum mechanics
— We study the effect of solvent viscosity on the kinetics of the photocycle of bacteriorhodopsin (bR) from Halobacterium halobium. Solvent viscosity is altered by changing the glycerol concentration from 20 to 80% glycerol by volume. The kinetics of the photocycle are observed after flash photolysis at four wavelengths at several temperatures between 240 and 315 K. Assuming a sequential model, bR → K ‐→ L → M → O → bR, Arrhenius plots of the rate coefficients determine the activation enthalpies and frequency factors for each step. Kinetic data from all solvents are considered together and studied as a function of temperature for fixed solvent viscosities. The early steps of the cycle are insensitive to solvent viscosity, →; the later steps are retarded with increasing viscosity. Activation enthalpies are independent of viscosity; the frequency factors are proportional to η −K , where the exponent k 0.25 for the transition K → L, 0.0 for L → M, 0.8 for M → O and 0.5 for O → bR.