Selective formation of oxindole- and formylkynurenine-type products from tryptophan and its peptides treated with a superoxide-generating system in the presence of iron(III)-EDTA: a possible involvement with iron-oxygen complex.
The oxygenation of tryptophan and its peptides by the superoxide-generating system hypoxanthine/xanthine oxidase in the presence of iron(III) and ethylenediaminetetraacetic acid (EDTA) has been investigated. The reaction of a tryptophan derivative, N-(tert-butoxycarbonyl)-L-tryptophan, with hypoxanthine/xanthine oxidase/Fe(III)-EDTA mainly resulted in the oxygenation of the pyrrole ring of the indole nucleus. 2-[(tert-Butoxycarbonyl)-amino]-3-(3-oxindolyl)propionic acid and N-(tert-butoxycarbonyl)-N'-formylkynurenine were identified as the major products. Similar oxindole- and formylkynurenine-type products were also obtained from the N-(tert-butoxycarbonyl) derivative of the tryptophan-containing peptides Ile-Trp, Trp-Leu, Gly-Trp-Leu, and Ala-Trp-Ile. In all cases, however, hydroxylation products of the benzene ring of the indole nucleus were scarcely detected, leading to the assumption that free hydroxyl radical did not play a role in the tryptophan oxidation of this system. Of interest was the fact that the reaction of N-(tert-butoxycarbonyl)-L-tryptophan with H2O2/horseradish peroxidase mainly afforded the same oxindole- and formylkynurenine-type products as those obtained in the hypoxanthine/xanthine oxidase/Fe(III)-EDTA system. Taken together, iron-oxygen complex-type active species may play a role in the tryptophan oxygenation in a superoxide-generating system in the presence of iron-EDTA.
Itakura
K
K
Department of Applied Biological Sciences, Nagoya University, Japan.
Uchida
K
K
Kawakishi
S
S
D000595:Amino Acid Sequence; D004492:Edetic Acid / Q000737:chemistry*; D005290:Ferric Compounds / Q000737:chemistry*; D007211:Indoles / Q000138:chemical synthesis*; D007502:Iron Chelating Agents / Q000737:chemistry; D007737:Kynurenine / Q000031:analogs & derivatives* / Q000138:chemical synthesis; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry; D013481:Superoxides / Q000737:chemistry; D014364:Tryptophan / Q000737:chemistry*
D005290:Ferric Compounds; D007211:Indoles; D007502:Iron Chelating Agents; D009842:Oligopeptides; C007772:N'-formylkynurenine; D013481:Superoxides; D007737:Kynurenine; D014364:Tryptophan; D004492:Edetic Acid; C019179:Fe(III)-EDTA; D010100:Oxygen