title: Direct demonstration of the presence of coordinated sulfate in the reaction pathway of Arabidopsis thaliana sulfite oxidase using 33S labeling and ESEEM spectroscopy.
abstract: Sulfite oxidase from Arabidopsis thaliana has been reduced at pH = 6 with sulfite labeled with 33S (nuclear spin I = 3/2), followed by reoxidation by ferricyanide to generate the Mo(V) state of the active center. To obtain information about the hyperfine interaction (hfi) of 33S with Mo(V), continuous-wave electron paramagnetic resonance (EPR) and electron spin echo envelope modulation (ESEEM) experiments have been performed. The interpretation of the EPR and ESEEM spectra was facilitated by a theoretical analysis of the nuclear transition frequencies expected for the situation of the nuclear quadrupole interaction being much stronger than the Zeeman and hyperfine interactions. The isotropic hfi constant of 33S determined in these experiments was about 3 MHz, which demonstrates the presence of coordinated sulfate in the sulfite-reduced low-pH form of the plant enzyme.
authors.affiliation: Department of Chemistry, University of Arizona, Tucson, Arizona 85721-0041, USA. andrei@u.arizona.edu
authors.forename: Andrei V
authors.initials: AV
authors.lastname: Astashkin
authors.forename: Kayunta
authors.initials: K
authors.lastname: Johnson-Winters
authors.forename: Eric L
authors.initials: EL
authors.lastname: Klein
authors.forename: Robert S
authors.initials: RS
authors.lastname: Byrne
authors.forename: Russ
authors.initials: R
authors.lastname: Hille
authors.forename: Arnold M
authors.initials: AM
authors.lastname: Raitsimring
authors.forename: John H
authors.initials: JH
authors.lastname: Enemark
mesh_terms: D017360:Arabidopsis / Q000201:enzymology* / Q000378:metabolism; D003198:Computer Simulation; D004578:Electron Spin Resonance Spectroscopy; D008872:Microwaves; D015394:Molecular Structure; D013431:Sulfates / Q000737:chemistry* / Q000378:metabolism*; D050876:Sulfite Oxidase / Q000378:metabolism*; D013460:Sulfur Isotopes
chemical_list: D013431:Sulfates; D013460:Sulfur Isotopes; D050876:Sulfite Oxidase