Protein structural change at the cytoplasmic surface as the cause of cooperativity in the bacteriorhodopsin photocycle

G. Váró, Richard Needleman, Janos K. Lanyi

Research output: Contribution to journalArticle

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Abstract

The effects of excitation fight intensity on the kinetics of the bacteriorhodopsin photocycle were investigated. The earlier reported intensity-dependent changes at 410 and 570 nm are explained by parallel increases in two of the rate constants, for proton transfers to D96 from the Schiff base and from the cytoplasmic surface, without changes in the others, as the photoexcited fraction is increased. Thus, it appears that the pK(a) of D96 is raised by a cooperative effect within the purple membrane. This interpretation of the wild-type kinetics was confirmed by results with several mutant proteins, where the rates are well separated in time and a model-dependent analysis is unnecessary. Based on earlier results that demonstrated a structural change of the protein after deprotonation of the Schiff base that increases the area of the cytoplasmic surface, and the effects of high hydrostatic pressure and lowered water activity on the photocycle steps in question, we suggest that the pK(a) of D96 is raised by a lateral pressure that develops when other bacteriorhodopsin molecules are photoexcited within the two-dimensional lattice of the purple membrane. Expulsion of no more than a few water molecules bound near D96 by this pressure would account for the calculated increase of 0.6 units in the pK(a).

Original languageEnglish
Pages (from-to)461-467
Number of pages7
JournalBiophysical Journal
Volume70
Issue number1
Publication statusPublished - Jan 1996

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Purple Membrane
Bacteriorhodopsins
Schiff Bases
Pressure
Hydrostatic Pressure
Water
Mutant Proteins
Protons
Proteins

ASJC Scopus subject areas

  • Biophysics

Cite this

Protein structural change at the cytoplasmic surface as the cause of cooperativity in the bacteriorhodopsin photocycle. / Váró, G.; Needleman, Richard; Lanyi, Janos K.

In: Biophysical Journal, Vol. 70, No. 1, 01.1996, p. 461-467.

Research output: Contribution to journalArticle

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