title: Kinetics of the competitive degradation of deoxyribose and other biomolecules by hydroxyl radicals produced by the Fenton reaction.
abstract: The objective of this work is to reexamine the competitive degradation of deoxyribose by hydroxyl radicals (.OH) produced by the reaction between H2O2 and Fe(2+)-EDTA. The .OH radicals produced attack deoxyribose (D, rate constant kD) and eventually an .OH scavenger (S, rate constant kS). First, we examined the effect of [D], [H2O2], [Fe(2+)-EDTA], [EDTA]/[Fe2+] ratio and reaction time on the rate of D degradation, measured as the absorbance of the chromogen formed between the product of the reaction D + .OH (malondialdehyde) and thiobarbituric acid. In particular, it was showed that under our experimental conditions ([D] = 3 mM, [H2O2] = 0.85 mM, [Fe2+] = 0.13 mM), the rate of overall process is first order in Fe2+, zero order in H2O2 and is maximal for a ratio [EDTA]/[Fe2+] = 1.1. Second, the kinetics of .OH radical reaction in competition experiments between D and S (mannitol) was investigated. The results show that the ratio of the rates of D degradation in the absence (VD) and in the presence (VDS) of S should be represented by VD/VDS = 1 + ks[S]/(kD[D] + kx) where kx accounts for the rate of .OH reactions with other reagents such as Fe(2+)-EDTA, H2O2 etc . . . After having determined kx for each set of experimental conditions, we obtained the values of kS/kD by determining the variations of VD/VDS as a function of [S] and [D]. By taking kD = 1.9 x 10(9) M-1s-1 a value of kS = 1.9 x 10(9) M-1s-1 was obtained, very close to that obtained by pulse radiolysis. Finally, the validity of the established relation was confirmed for other biomolecules (methionine, k = 5.6 x 10(9)M-1s-1 and alanine, k = 3.3 x 10(8) M-1s-1). By contrast, it was not applicable to cysteine, thiourea and mercaptoethanol which was attributed to an interaction of the latter scavengers with Fe2+ and/or H2O2.
authors.affiliation: Laboratoire de Chimie Thérapeutique, Faculté de Pharmacie, Illkirch France.
authors.forename: M J
authors.initials: MJ
authors.lastname: Zaho
authors.forename: L
authors.initials: L
authors.lastname: Jung
authors.forename: C
authors.initials: C
authors.lastname: Tanielian
authors.forename: R
authors.initials: R
authors.lastname: Mechin
mesh_terms: D000596:Amino Acids / Q000737:chemistry; D001205:Ascorbic Acid / Q000737:chemistry; D002863:Chromogenic Compounds; D003855:Deoxyribose / Q000737:chemistry*; D004492:Edetic Acid; D005296:Ferrous Compounds; D006861:Hydrogen Peroxide; D017665:Hydroxyl Radical; D007700:Kinetics; D008315:Malondialdehyde / Q000737:chemistry*; D008353:Mannitol; D013455:Sulfur / Q000737:chemistry; D013858:Thiobarbiturates / Q000737:chemistry*
chemical_list: D000596:Amino Acids; D002863:Chromogenic Compounds; D005296:Ferrous Compounds; D013858:Thiobarbiturates; D017665:Hydroxyl Radical; D008353:Mannitol; D008315:Malondialdehyde; D003855:Deoxyribose; D013455:Sulfur; D004492:Edetic Acid; D006861:Hydrogen Peroxide; C029684:thiobarbituric acid; D001205:Ascorbic Acid