title: High catalytic activity achieved with a mixed manganese-iron site in protein R2 of Chlamydia ribonucleotide reductase.
abstract: Ribonucleotide reductase (class I) contains two components: protein R1 binds the substrate, and protein R2 normally has a diferric site and a tyrosyl free radical needed for catalysis. In Chlamydia trachomatis RNR, protein R2 functions without radical. Enzyme activity studies show that in addition to a diiron cluster, a mixed manganese-iron cluster provides the oxidation equivalent needed to initiate catalysis. An EPR signal was observed from an antiferromagnetically coupled high-spin Mn(III)-Fe(III) cluster in a catalytic reaction mixture with added inhibitor hydroxyurea. The manganese-iron cluster in protein R2 confers much higher specific activity than the diiron cluster does to the enzyme.
authors.affiliation: Department of Biochemistry and Biophysics, Stockholm University, SE-10691 Stockholm, Sweden.
authors.forename: Nina
authors.initials: N
authors.lastname: Voevodskaya
authors.forename: Friedhelm
authors.initials: F
authors.lastname: Lendzian
authors.forename: Anders
authors.initials: A
authors.lastname: Ehrenberg
authors.forename: Astrid
authors.initials: A
authors.lastname: Gräslund
mesh_terms: D002384:Catalysis; D002692:Chlamydia trachomatis / Q000201:enzymology* / Q000235:genetics; D004578:Electron Spin Resonance Spectroscopy; D007501:Iron / Q000737:chemistry* / Q000378:metabolism*; D008345:Manganese / Q000737:chemistry* / Q000378:metabolism*; D012264:Ribonucleotide Reductases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: D008345:Manganese; D007501:Iron; D012264:Ribonucleotide Reductases