The horseradish peroxidase catalysed oxidation of deoxyribose sugars

The ability of horseradish peroxidase (E.C. 1.11.1.7, Donor: H2O2 oxidoreductase) to catalytically oxidize 2-deoxyribose sugars to a free radical species was investigated. The ESR spin-trapping technique was used to demonstrate that free radical species were formed. Results with the spin trap 3,5-dibromo-4-nitrosobenzene sulphonic acid showed that horseradish peroxidase can catalyse the oxidation of 2-deoxyribose to produce an ESR spectrum characteristic of a nitroxide radical spectrum. This spectrum was shown to be a composite of spin adducts resulting from two carbon-centered species, one spin adduct being characterized by the hyperfine coupling constants aN = 13.6 G and aH beta = 11.0 G, and the other by aN = 13.4 G and aH beta = 5.8 G. When 2-deoxyribose-5-phosphate was used as the substrate, the spectrum produced was found to be primarily one species characterized by the hyperfine coupling constants aN = 13.4 G and aH beta = 5.2. All the radical species produced were carbon-centered spin adducts with a beta hydrogen, suggesting that oxidation occurred at the C(2) or C(5) moiety of the sugar. Interestingly, it was found that under the same experimental conditions, horseradish peroxidase apparently did not catalyze the oxidation of either 3-deoxyribose or D-ribose to a free radical since no spin adducts were found in these cases.