Dec 22, 1999

Conformationally controlled pK-switching in membrane proteins: one more mechanism specific to the enzyme catalysis?

FEBS Letters
A Y Mulkidjanian

Abstract

Internal proton displacements in several membrane photosynthetic enzymes are analyzed in relation to general mechanisms of enzymatic catalysis. In the bacterial photosynthetic reaction center (RC) and in bacteriorhodopsin (BR), carboxy residues (Glu-212 in the RC L-subunit and Asp-96 in BR) serve as indispensable intrinsic proton donors. Both carboxyls are protonated prior to the proton-donation step, because their pK values are shifted to >/=12.0 by the interaction with the protein and/or substrate. In both cases, the proton transfer reactions are preceded by conformational changes that, supposedly, let water interact with the carboxyls. These changes switch over the pK values of the carboxyls to </=6.0 and 7.1 in the RC and BR, respectively. The sharp increase in the proton-donating ability of the carboxyls drives the reaction cycles. This kind of catalytic mechanism, where a strong general acid or base emerges, when needed, as a result of a conformational change can be denoted as a conformationally controlled pK-switching. Generally, the ability of enzymes to go between isoenergetic conformations that differ widely in the reactivity of the catalytic group(s) may be of crucial importance to the understanding of enzymatic cata...Continue Reading

Mentioned in this Paper

Ubiquinone (Lab Procedure)
Benzoquinone
Photosynthetic Reaction Centers
Bacteriorhodopsins
Histidine
Enzymes, antithrombotic
Quinones
Ubiquinol
Resting Potentials
Plain X-ray

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