title: Resonance Raman spectroscopic characterization of the molybdopterin active site of DMSO reductase.
abstract: Resonance Raman spectra are compared for Rhodobacter sphaeroides dimethyl sulfoxide reductase, an enzyme containing a molybdopterin cofactor, and two model compounds, I and II, which have pterin and quinoxaline, respectively, attached to a Cp2Mo[IV]-dithiolene chelate [Cp = cyclopentadienyl]. The effect of 34S incorporation was also determined. Several bands in the 200-500 cm-1 region show remarkably similar patterns of frequencies and isotope shifts between protein and models: a band at 351 cm-1 shifts 6-8 cm-1, and bands at lower and higher frequencies show smaller shifts upon 34S substitution. A normal coordinate analysis on II indicates the 351 cm-1 mode to be the symmetric Mo-S[dithiolene] stretch and the remaining low-frequency modes to contain contributions from deformations of the quinoxaline ring as well as from Mo-S stretching. The similarity in the low-frequency spectra between the model compounds and the enzyme strongly supports a dithiolene chelate as the mode of Mo-pterin interaction in the cofactor. Resonance enhancement of both high- and low-frequency quinoxaline or pterin modes is observed for both model compounds, implicating the heterocyclic rings as part of the electronic system involved in the Mo-dithiolene charge transfer transitions. RR spectra of 6-methylpterin and biopterin are reported and used to identify the pterin and quinoxaline high-frequency bands in the model compound spectra. The dithiolene C = C stretch is tentatively assigned to bands at 1506 cm-1 in I and 1515 cm-1 in II.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Chemistry, Princeton University, New Jersey 08544.
authors.forename: L
authors.initials: L
authors.lastname: Kilpatrick
authors.forename: K V
authors.initials: KV
authors.lastname: Rajagopalan
authors.forename: J
authors.initials: J
authors.lastname: Hilton
authors.forename: N R
authors.initials: NR
authors.lastname: Bastian
authors.forename: E I
authors.initials: EI
authors.lastname: Stiefel
authors.forename: R S
authors.initials: RS
authors.lastname: Pilato
authors.forename: T G
authors.initials: TG
authors.lastname: Spiro
mesh_terms: D001665:Binding Sites; D003067:Coenzymes / Q000737:chemistry / Q000378:metabolism; D007506:Iron-Sulfur Proteins; D008667:Metalloproteins / Q000737:chemistry*; D008956:Models, Chemical; D015394:Molecular Structure; D008982:Molybdenum / Q000737:chemistry; D000090006:Molybdenum Cofactors; D010088:Oxidoreductases / Q000737:chemistry* / Q000378:metabolism; D011489:Protein Denaturation; D011621:Pteridines / Q000737:chemistry*; D011622:Pterins / Q000737:chemistry; D012242:Rhodobacter sphaeroides / Q000201:enzymology; D013053:Spectrophotometry; D013059:Spectrum Analysis, Raman
chemical_list: D003067:Coenzymes; D007506:Iron-Sulfur Proteins; D008667:Metalloproteins; D008982:Molybdenum; D000090006:Molybdenum Cofactors; D010088:Oxidoreductases; D011621:Pteridines; D011622:Pterins; C022261:molybdopterin; C045664:dimethyl sulfoxide reductase