Equilibrium and kinetic parameters for the binding of inhibitors to the QB pocket in bacterial chromatophores: dependence on the state of QA

Biochemistry
N Ginet, J Lavergne

Abstract

The equilibrium and kinetic parameters for the binding of various inhibitors to the Q(B) pocket of the bacterial reaction center were investigated in chromatophores from Rhodobacter capsulatus and Rhodobacter sphaeroides. By monitoring the near-IR absorption changes specific to Q(A)(-) and Q(B)(-), we measured the fraction of inhibited centers in the dark and the kinetics and extent of inhibitor displacement after one flash due to the formation of the Q(A)Q(B)(-) state. The inhibitor release rate was much faster for triazines and o-phenanthroline (t(1/2) in the 50 ms to 1 s range) than for stigmatellin (t(1/2) approximately 20 s). For inhibitors with a rapid release rate, the fast phase of P(+) decay observed in the absence of secondary donor reflects the competition between P(+)Q(A)(-) recombination and inhibitor release: it is thus faster than the P(+)Q(A)(-) recombination, and its relative extent is smaller than the fraction of initially inhibited centers. At appropriate inhibitor concentrations, one can have almost total binding in the dark and almost total inhibitor displacement after one flash. Under such conditions, a pair of closely spaced flashes resets the two-electron gate in a single state (Q(A)Q(B)(-)), irrespectiv...Continue Reading

Citations

May 12, 2009·Proceedings of the National Academy of Sciences of the United States of America·Barbara Schoepp-CothenetWolfgang Nitschke
May 2, 2002·Proceedings of the National Academy of Sciences of the United States of America·J TandoriL Baciou
Dec 18, 2007·FEBS Letters·Maria A KozlovaArmen Y Mulkidjanian
Jan 22, 2015·Biophysical Journal·László GerencsérPéter Maróti
Sep 16, 2004·Chembiochem : a European Journal of Chemical Biology·Nicola D'AmelioWolfgang Lubitz
Apr 11, 2003·Biochimica Et Biophysica Acta·Arthur G RobertsDavid M Kramer
Oct 7, 2016·Photosynthesis Research·Tibor SzabóLászló Nagy
Nov 25, 2005·Journal of Fluorescence·Graham HungerfordM Elisabete C D Real Oliveira

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