title: Thiyl radicals in ribonucleotide reductases.
abstract: The ribonucleoside triphosphate reductase (RTPR) from Lactobacillus leichmannii catalyzes adenosylcobalamin (AdoCbl)-dependent nucleotide reduction, as well as exchange of the 5' hydrogens of AdoCbl with solvent. A protein-based thiyl radical is proposed as an intermediate in both of these processes. In the presence of RTPR containing specifically deuterated cysteine residues, the electron paramagnetic resonance (EPR) spectrum of an intermediate in the exchange reaction and the reduction reaction, trapped by rapid freeze quench techniques, exhibits narrowed hyperfine features relative to the corresponding unlabeled RTPR. The spectrum was interpreted to represent a thiyl radical coupled to cob(II)alamin. Another proposed intermediate, 5'-deoxyadenosine, was detected by rapid acid quench techniques. Similarities in mechanism between RTPR and the Escherichia coli ribonucleotide reductase suggest that both enzymes require a thiyl radical for catalysis.
authors.affiliation: Department of Chemistry, Massachusetts Institute of Technology, Cambridge 02139, USA.
authors.forename: S
authors.initials: S
authors.lastname: Licht
authors.forename: G J
authors.initials: GJ
authors.lastname: Gerfen
authors.forename: J
authors.initials: J
authors.lastname: Stubbe
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000595:Amino Acid Sequence; D002384:Catalysis; D003038:Cobamides / Q000378:metabolism; D003839:Deoxyadenosines / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals; D007700:Kinetics; D007778:Lactobacillus / Q000201:enzymology; D008024:Ligands; D008956:Models, Chemical; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D012264:Ribonucleotide Reductases / Q000737:chemistry / Q000378:metabolism*; D012997:Solvents; D013438:Sulfhydryl Compounds / Q000378:metabolism*; D014805:Vitamin B 12 / Q000031:analogs & derivatives / Q000378:metabolism
chemical_list: D003038:Cobamides; D003839:Deoxyadenosines; D005609:Free Radicals; D008024:Ligands; D012997:Solvents; D013438:Sulfhydryl Compounds; C097751:cob(II)alamin; C033714:5'-deoxyadenosine; D000255:Adenosine Triphosphate; D012264:Ribonucleotide Reductases; C000913:cobamamide; D014805:Vitamin B 12