title: The hydroxylation of tryptophan.
abstract: Products of the chemical hydroxylation of tryptophan by Fenton and Udenfriend reactions are similar to those obtained by ionizing radiation. When tryptophan is exposed to either of these systems, a mixture of four hydroxytryptophans, oxindole-3-alanine, and N-formylkynurenine is formed. This observation indicates that the hydroxyl radical attacks the aromatic nucleus as well as the 2 and 3 positions of the pyrrole ring. During gamma-radiolysis of nitrous oxide-saturated tryptophan solution and in the absence of oxygen or ferric edta, the hydroxyl radical adduct (or hydroxycyclohexadienyl radical) of tryptophan undergoes dimerization and polymerization, which results in a yellow product with maximal absorbance at 425 nm. In the presence of ferric edta, or in a Fenton system, the hydroxyl radical adduct disproportionates, and hydroxylated derivatives are formed. The yields of the hydroxytryptophans are proportional to the concentration of ferric edta to a limiting yield of 54% of the theoretical yield, which is taken to be one hydroxylated product per two hydroxyl radicals. Under these conditions, 4-, 5-, 6-, and 7-hydroxy-derivatives of tryptophan are found in the proportion 4:2:2:3, respectively. The presence of dioxygen during gamma-radiolysis increases the yield of N-formylkynurenine, but does not affect the total yield of hydroxytryptophans. Similarly, tryptophan subjected to the Udenfriend reaction yields 4-, 5-, 6-, and 7-hydroxytryptophan and N-formylkynurenine in approximately equal amounts.
authors.affiliation: Biodynamics Institute, Louisiana State University, Baton Rouge 70803-1800.
authors.forename: Z
authors.initials: Z
authors.lastname: Maskos
authors.forename: J D
authors.initials: JD
authors.lastname: Rush
authors.forename: W H
authors.initials: WH
authors.lastname: Koppenol
mesh_terms: D001205:Ascorbic Acid; D002851:Chromatography, High Pressure Liquid; D004492:Edetic Acid / Q000494:pharmacology; D005290:Ferric Compounds / Q000494:pharmacology; D005720:Gamma Rays; D006861:Hydrogen Peroxide; D006863:Hydrogen-Ion Concentration; D006878:Hydroxides / Q000378:metabolism; D017665:Hydroxyl Radical; D006900:Hydroxylation; D007501:Iron; D007737:Kynurenine / Q000031:analogs & derivatives / Q000378:metabolism; D046911:Macromolecular Substances; D009609:Nitrous Oxide; D010100:Oxygen; D010777:Photochemistry; D011675:Pulse Radiolysis; D013053:Spectrophotometry; D014364:Tryptophan / Q000378:metabolism*
chemical_list: C045076:Fenton's reagent; D005290:Ferric Compounds; D006878:Hydroxides; D046911:Macromolecular Substances; C007772:N'-formylkynurenine; D017665:Hydroxyl Radical; D007737:Kynurenine; D014364:Tryptophan; D004492:Edetic Acid; D006861:Hydrogen Peroxide; D007501:Iron; D009609:Nitrous Oxide; C019179:Fe(III)-EDTA; D001205:Ascorbic Acid; D010100:Oxygen