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On the Oxygen Reactivity of Flavoprotein Oxidases

L. Piubelli,M. Pedotti,G. Molla,Susanne Feindler-Boeckh,S. Ghisla,M. Pilone,L. Pollegioni

Published 2008 in Journal of Biological Chemistry

ABSTRACT

The flavoprotein cholesterol oxidase from Brevibacterium sterolicum (BCO) possesses a narrow channel that links the active center containing the flavin to the outside solvent. This channel has been proposed to serve for the access of dioxygen; it contains at its “bottom” a Glu-Arg pair (Glu-475—Arg-477) that was found by crystallographic studies to exist in two forms named “open” and “closed,” which in turn was suggested to constitute a gate functioning in the control of oxygen access. Most mutations of residues that flank the channel have minor effects on the oxygen reactivity. Mutations of Glu-311, however, cause a switch in the basic kinetic mechanism of the reaction of reduced BCO with dioxygen; wild-type BCO and most mutants show a saturation behavior with increasing oxygen concentration, whereas for Glu-311 mutants a linear dependence is found that is assumed to reflect a “simple” second order process. This is taken as support for the assumption that residue Glu-311 finely tunes the Glu-475—Arg-477 pair, forming a gate that functions in modulating the access/reactivity of dioxygen.

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