Mechanistic studies of a protonolytic organomercurial cleaving enzyme: bacterial organomercurial lyase

Journal Article · Tue Nov 04 04:00:00 EST 1986 · Biochemistry; (United States)

DOI:https://doi.org/10.1021/bi00370a064· OSTI ID:6698699

Begley, T P; Walts, A E; Walsh, C T

Studies with stereochemically defined substrates cis-2-butenyl-2-mercuric chloride (1) and endo-norbornyl-2-mercuric bromide (2) reveal that a high degree of configurational retention occurs during the bond cleavage, while studies with exo-3-acetoxynortricyclyl-5-mercuric bromide (3) and cis-exo-2-acetoxy-bicyclo(2.2.1)hept-5-enyl-3-mercuric bromide (4) show that the protonolysis proceeds without accompanying skeletal rearrangement. Kinetic data for the enzymatic reactions of cis-2-butenyl-2-mercuric chloride (1) and trans-1-propenyl-1-mercuric chloride (6) indicate that these substrates show enhanced reaction rates of ca. 10-200-fold over alkylvinylmercurials and unsubstituted vinylmercurials, suggesting that the olefinic methyl substituent may stabilize an intermediate bearing some positive charge. Enzymatic reaction of 2-butenyl-1-mercuric bromide (5) yields a 72/23/5 mixture of 1-butene/trans-2-butene/cis-2-butene, indicative of intervening SE2' cleavage. The observation of significant solvent deuterium isotope effects at pH 7.4 of Vmax (H/sub 2/O)/Vmax(D/sub 2/O) = 2.1 for cis-2-butenyl-2-mercuric chloride (1) turnover and Vmax(H/sub 2/O)/Vmax(D/sub 2/O) = 4.9 for ethylmercuric chloride turnover provides additional support for a kinetically important proton delivery. Finally, the stoichiometric formation of butene and Hg(II) from 1 and methane and Hg(II) from methylmercuric chloride eliminates the possibility of an SN1 solvolytic mechanism. As the first well-characterized enzymatic reaction of an organometallic substrate and the first example of an enzyme-mediated SE2 reaction the organomercurial lyase catalyzed carbon-mercury bond cleavage provides an arena for investigating novel enzyme structure-function relationships.

• Research Organization: Massachusetts Institute of Technology, Cambridge
• OSTI ID: 6698699
• Journal Information: Biochemistry; (United States), Journal Name: Biochemistry; (United States) Vol. 22; ISSN BICHA
• Country of Publication: United States
• Language: English

Related Subjects

560300* -- Chemicals Metabolism & Toxicology
63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.
BACTERIA
BIOCHEMICAL REACTION KINETICS
BROMIDES
BROMINE COMPOUNDS
CHLORIDES
CHLORINE COMPOUNDS
DEUTERIUM COMPOUNDS
ENZYME ACTIVITY
ENZYMES
ESCHERICHIA COLI
HALIDES
HALOGEN COMPOUNDS
HYDROGEN COMPOUNDS
KINETICS
LYASES
MERCURY BROMIDES
MERCURY CHLORIDES
MERCURY COMPOUNDS
MERCURY HALIDES
METABOLISM
MICROORGANISMS
ORGANIC COMPOUNDS
ORGANIC MERCURY COMPOUNDS
REACTION KINETICS
STOICHIOMETRY
STRUCTURE-ACTIVITY RELATIONSHIPS