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Mechanism of mercury(II) reductase and influence of ligation on the reduction of mercury(II) by a water soluble 1,5-dihydroflavin.

Proceedings of the National Academy of Sciences of the United States of America (1989-05-01)
E Gopinath, T W Kaaret, T C Bruice
ABSTRACT

The nature and rate of reduction of Hg2+ to Hg0 by 1,5-dihydro-3,(3-sulfopropyl)lumiflavin (FIH2) in buffered aqueous solutions (pH 4.7) is dependent on the ligation of Hg2+. In the presence of N,N-bis(2-hydroxyethyl)glycine or when ligated to ethylenediaminetetraacetic acid, the reduction is first order in Hg2+ and FIH2. The apparent second-order rate constant with N,N-bis(2-hydroxyethyl)glycine (2.2 x 10(6) M-1.s-1) is much greater than that in the presence of ligating ethylenediaminetetraacetic acid (1.5 x 10(2) M-1.s-1). When ligated by mercaptoethanesulfonate, reduction of Hg2+ by FIH2 is characterized by a pronounced lag phase, which is dependent on the concentration of mercaptoethanesulfonate. The rate decreases with increase in mercaptoethanesulfonate, and with an excess of 10 equivalents, Hg2+ is not reduced by FIH2. These observations show that bis-ligation by thiolate greatly decreases the reducibility of Hg2+ and that further ligation by thiolate further retards the reaction. Comparison of oxidation-reduction potentials at various pH values shows that bis-ligation (or greater) of Hg2+ by thiolate substantially lowers the reduction potential of Hg2+ below that of 3(3-sulfopropyl)lumiflavin (FIox). Thus, the ease of reduction of Hg2+ complexes by FIH2 decreases with increasing thermodynamic stability of the complex. These results do not support the proposed role of the thiol functionalities in facilitating the mercury(II) reductase (Hg:NADP+ oxidoreductase, EC 1.16.1.1)-catalyzed reduction of Hg2+ through tris- or tetraligation of Hg2+.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
BICINE, ≥99% (titration)
Sigma-Aldrich
BICINE, BioXtra, ≥99% (titration)
SAFC
Bicine, PharmaGrade, Manufactured under appropriate controls for use as a raw material in pharma or biopharmaceutical production., suitable for cell culture

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