title: A DNA oligonucleotide-hemin complex cleaves t-butyl hydroperoxide through a homolytic mechanism.
abstract: Both electron paramagnetic resonance (EPR) and electronic absorption spectroscopy have been employed to investigate the reaction of a guanine-rich DNA nucleotide-hemin complex (PS2.M-hemin complex) and organic peroxide (t-Bu-OOH). Incubation of the PS2.M-hemin complex with t-Bu-OOH resulted in the time-dependent decrease in the heme Soret with concomitant changes to the visible bands of the electronic absorbance spectrum for the PS2.M-hemin complex. Parallel EPR studies using the spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO) combined with spectral simulation demonstrated the presence of tert-butyloxyl, carbon-centered methyl, and methyl peroxyl radicals as well as a simple nitroxide (triplet) signal. Experiments, performed by maintaining a constant ratio of t-Bu-OOH/PS2.M-hemin complex ( approximately 35 mol/mol) while varying DMPO concentration, indicated that the relative contributions of each radical adduct to the composite EPR spectrum were significantly influenced by the DMPO concentration. For example, at DMPO/PS2.M-hemin of 10-50 mol/mol, a complex mixture of radicals was consistently detected, whereas at high trapping efficiency (i.e., DMPO/PS2.M-hemin of approximately 250 mol/mol) the tert-butyloxyl-DMPO adduct was predominant. In contrast, at relatively low DMPO/PS2.M-hemin complex ratios of < or =5 mol/mol, a simple nitroxide three-line EPR signal was detected largely in the absence of all other radicals. Together, these data indicate that tert-butyloxyl radical is the primary radical likely formed from the homolytic cleavage of the O-O peroxy bond of t-Bu-OOH, while methyl and methyl peroxyl radicals result from beta-scission of the primary tert-butyloxyl radical product.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada.
authors.forename: P K
authors.initials: PK
authors.lastname: Witting
authors.forename: P
authors.initials: P
authors.lastname: Travascio
authors.forename: D
authors.initials: D
authors.lastname: Sen
authors.forename: A G
authors.initials: AG
authors.lastname: Mauk
mesh_terms: D004247:DNA / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D006420:Hemeproteins / Q000737:chemistry; D006427:Hemin / Q000737:chemistry*; D006868:Hydrolysis; D008956:Models, Chemical; D009838:Oligodeoxyribonucleotides / Q000737:chemistry*; D010545:Peroxides; D013053:Spectrophotometry; D020122:tert-Butylhydroperoxide / Q000737:chemistry*
chemical_list: D006420:Hemeproteins; D009838:Oligodeoxyribonucleotides; D010545:Peroxides; C049375:perhydroxyl radical; D006427:Hemin; D004247:DNA; D020122:tert-Butylhydroperoxide