Indole-3-pyruvic and -propionic acids, kynurenic acid, and related metabolites as luminophores and free-radical scavengers.
Chemiluminescence associated with oxidation by free radicals was investigated in an alkaline, hemin-catalysed hydrogen peroxide system, using the following tryptophan metabolites as radical scavengers: indole-3-pyruvic, indole-3-propionic, kynurenic, xanthurenic and quinaldic acids and 4-hydroxy-quinoline. Light emission from oxidation of the indolic compounds was only partially inhibited by the hydroxyl-radical scavenger DMSO, but strongly suppressed by the superoxide-anion scavenger Tiron, whereas chemi-luminescence generated from kynurenic acid was strongly inhibited by either of these compounds. Light emission from oxidation of kynurenic acid lasts for a surprisingly long period of time: At 0.4 mM and 20 degrees C, luminescence increased for 5 hours and continued at a high rate for more than a day. Comparison of structural analogues indicated that the 4-hydroxyl and carboxyl groups of kynurenic acid are essential for effective light emission, and that an additional 8-hydroxyl residue leading to an intramolecular hydrogen bond diminishes the reaction rate.
Hardeland
R
R
Institut für Zoologie und Anthropologie, Universität Göttingen, Germany.
Zsizsik
B K
BK
Poeggeler
B
B
Fuhrberg
B
B
Holst
S
S
Coto-Montes
A
A
D004121:Dimethyl Sulfoxide; D016166:Free Radical Scavengers / Q000737:chemistry*; D007202:Indicators and Reagents; D007211:Indoles / Q000737:chemistry*; D007700:Kinetics; D007736:Kynurenic Acid / Q000737:chemistry*; D008163:Luminescent Measurements; D010084:Oxidation-Reduction
D016166:Free Radical Scavengers; D007202:Indicators and Reagents; D007211:Indoles; C008122:indol-3-yl pyruvic acid; C015292:indolepropionic acid; D007736:Kynurenic Acid; D004121:Dimethyl Sulfoxide