title: Catalysis by desolvation: the catalytic prowess of SAM-dependent halide-alkylating enzymes.
abstract: In the biological fixation of halide ions, several enzymes have been found to catalyze alkyl transfer from S-adenosylmethionine to halide ions. It proves possible to measure the rates of reaction of the trimethylsulfonium ion with I(-), Br(-), Cl(-), F(-), HO(-), and H2O in water at elevated temperatures. Comparison of the resulting second-order rate constants, extrapolated to 25 °C, with the values of k(cat)/K(m) reported for fluorinase and chlorinase indicates that these enzymes enhance the rates of alkyl halide formation by factors of 2 × 10(15)- and 1 × 10(17)-fold, respectively. These rate enhancements, achieved without the assistance of cofactors, metal ions, or general acid-base catalysis, are the largest that have been reported for an enzyme that acts on two substrates.
authors.affiliation: Department of Biochemistry and Biophysics, School of Medicine, University of North Carolina , Chapel Hill, North Carolina 27599, United States.
authors.forename: Danielle C
authors.initials: DC
authors.lastname: Lohman
authors.forename: David R
authors.initials: DR
authors.lastname: Edwards
authors.forename: Richard
authors.initials: R
authors.lastname: Wolfenden
mesh_terms: D000478:Alkylation; D000838:Anions / Q000737:chemistry / Q000378:metabolism; D001426:Bacterial Proteins / Q000378:metabolism*; D006219:Halogens / Q000737:chemistry / Q000378:metabolism*; D008848:Micromonosporaceae / Q000201:enzymology*; D010088:Oxidoreductases / Q000378:metabolism*; D012436:S-Adenosylmethionine / Q000378:metabolism*; D013302:Streptomyces / Q000201:enzymology*; D014867:Water / Q000737:chemistry / Q000378:metabolism
chemical_list: D000838:Anions; D001426:Bacterial Proteins; D006219:Halogens; D014867:Water; D012436:S-Adenosylmethionine; D010088:Oxidoreductases; C495766:fluorinase