Biophysical Journal 61: 1001-1006 (1992)
© 1992 the Biophysical Society

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Chizhov, I. Articles by Hess, B. Search for Related Content PubMed Articles by Chizhov, I. Articles by Hess, B.

Temperature and pH sensitivity of the O₆₄₀ intermediate of the bacteriorhodopsin photocycle

I. Chizhov ^*, M. Engelhard , D. S. Chernavskii , B. Zubov ^* and B. Hess 

General Physics Institute of the Academy of Sciences, USSR, 117942 Moscow, Union of Soviet Socialist Republics
Max-Planck-Institut für Ernährungsphysiologie, W-Dortmund, Germany
Physical Institute of the Academy of Sciences, USSR, 117333 Moscow, Union of Soviet Socialist Republics

ABSTRACT

The temperature and pH dependencies of the O₆₄₀ intermediate of the photocycle of bacteriorhodopsin (bR) were investigated by flash photolysis and T-jump experiments. The maximal concentration of the O₆₄₀ intermediate was found to be dependent on the temperature, which is described by a sigmoidal relationship. With increasing pH the midpoint of the sigmoidal curves shifts to higher temperatures. The Van't Hoff equation provides enthalpy and entropy values of the observed states. These results indicate that, in the investigated temperature (0-60°C) and pH (pH 4.0-10.0) range, the sequence of the principal intermediates in the pathway "M-N-O-bR" does not change. The observations of the O₆₄₀ intermediate at pH < 8.0 and of the N₅₅₀ intermediate at pH > 8.0 are most probably due only to changes of the intrinsic rate constants of the bR photocycle, not to a different mechanism.