Enzymatic catalysis of mercury methylation by Desulfovibrio desulfuricans LS

Journal Article · Fri Apr 01 00:00:00 EST 1994 · Applied and Environmental Microbiology; (United States)

OSTI ID:7199077

Choi, S C; Chase, T Jr; Bartha, R ^[1]

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1. Rutgers Univ., New Brunswick, NJ (United States)

The recently defined role of methylcobalamin in Hg[sup 2+] methylation by Desulfovibrio desulfuricans LS enabled us to reexamine the question of whether the principal source of methylmercury is spontaneous transmethylation or an enzymatically catalyzed process. In cell extracts of D. desulfuricans LS, over 95% of the [sup 57]Co label was associated with macromolecules rather than with free cobalamin. Both gel filtration and electrophoresis of cell extracts identified a single corrinoid protein of 40 kDa in size. This finding, in combination with the previously reported light-reversible propyl iodide inhibition of the Hg[sup 2+] methylation process, led us to propose that this 40-kDa corrinoid protein is the in vivo methyl donor in D. desulfuricans LS. Under reducing conditions, cell extracts containing the corrinoid protein produced [sup 14]CH[sub 3]Hg[sup +] from Hg[sup 2+] and 5-[sup 14]CH[sub 3[minus]] tetrahydrofolate with a maximum specific activity of 0.73 nmol min[sup [minus]1] mg of cell protein[sup [minus]1]. The sequence of methyl transfer was from methyltetrahydrofolate to the corrinoid protein to Hg[sup 2+]. The rate of methylation versus the Hg[sup 2+] concentration followed Michaelis-Menten kinetics, with an apparent K[sub m] of 0.87 mM HgCl[sub 2]. The activity was oxygen sensitive, and Hg[sup 2+] methylation was optimal at 35[degrees]C and pH 6.5. The observation of saturation kinetics and the 600-fold-higher rate of Hg[sup 2+] methylation (at pH 7.0) by cell extracts, compared with transmethylation by free methylcobalamin, proved that in vivo Hg[sup 2+] methylation is an enzymatically catalyzed process. 23 refs., 6 figs.

• OSTI ID: 7199077
• Journal Information: Applied and Environmental Microbiology; (United States), Vol. 60:4; ISSN 0099-2240
• Country of Publication: United States
• Language: English

Related Subjects

63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.
DESULFOVIBRIO
BIOCHEMISTRY
MERCURY
METHYLATION
CATALYSIS
ENZYMES
METHYLMERCURY
BACTERIA
CHEMICAL REACTIONS
CHEMISTRY
ELEMENTS
METALS
MICROORGANISMS
ORGANIC COMPOUNDS
ORGANIC MERCURY COMPOUNDS
PROTEINS
SULFATE-REDUCING BACTERIA
560300* - Chemicals Metabolism & Toxicology