ascorbic-acid and 3-hydroxykynurenine

The kynurenine pathway catabolite 3-hydroxykynurenine (3HK) and redox-active metals such as copper and iron are implicated in cataractogenesis. Here we investigate the reaction of kynurenine pathway catabolites with copper and iron, as well as interactions with the major lenticular structural proteins, the alpha-crystallins. The o-aminophenol kynurenine catabolites 3HK and 3-hydroxyanthranilic acid (3HAA) reduced Cu(II)>Fe(III) to Cu(I) and Fe(II), respectively, whereas quinolinic acid and the nonphenolic kynurenine catabolites kynurenine and anthranilic acid did not reduce either metal. Both 3HK and 3HAA generated superoxide and hydrogen peroxide in a copper-dependent manner. In addition, 3HK and 3HAA fostered copper-dependent alpha-crystallin cross-linking. 3HK- or 3HAA-modifed alpha-crystallin showed enhanced redox activity in comparison to unmodified alpha-crystallin or ascorbate-modified alpha-crystallin. These data support the possibility that 3HK and 3HAA may be cofactors in the oxidative damage of proteins, such as alpha-crystallin, through interactions with redox-active metals and especially copper. These findings may have relevance for understanding cataractogenesis and other degenerative conditions in which the kynurenine pathway is activated.

Topics: 3-Hydroxyanthranilic Acid; Animals; Ascorbic Acid; Cataract; Cattle; Copper; Crystallins; Electrochemistry; Humans; Hydrogen Peroxide; Iron; Kynurenine; Lens, Crystalline; Metals; Oxidation-Reduction; Superoxides; Tryptophan

We studied the distribution of O2-.-scavenging activity in 6-day-old larvae of Aldrichina grahami. Total activity was highest in the muscle. The specific activity per milligram of protein in the Malpighian tubules was highest, 10 times the highest elsewhere. Most of the O2-. scavenging activity in muscle depended on superoxide dismutase. However, the activity in the Malpighian tubules mostly depended on 3-hydroxykynurenine.

Topics: Animals; Ascorbic Acid; Chromatography, High Pressure Liquid; Diptera; Free Radicals; Kynurenine; Molecular Weight; Oxygen; Tissue Distribution; Uric Acid

3-Hydroxykynurenine is condensed to xanthommatin by cytochrome c and cytochrome oxidase in rat liver mitochondria. In intact mitochondria the reaction is inhibited by respiratory chain substrates. However, this was not the case with preincubated mitochondria or with isolated cytochrome c and cytochrome oxidase. The inhibition of xanthommatin formation in native mitochondria by succinate was abolished by addition of antimycin A or malonate, whereas the inhibition by citrate, glutamate or fumarate was not impaired by antimycin A or amobarbital. However, after preincubation of mitochondria at 37 degrees C for 30 min the inhibition disappeared in these cases too. It is suggested that the inhibition by succinate is due to the supply of reduced cytochrome b which competes with 3-hydroxykynurenine for ferricytochrome c, while the other respiratory chain substrates inhibit xanthommatin formation only in the case of intact mitochondria by a yet unknown mechanism. These inhibition mechanisms prevent xanthommatin formation in rat liver mitochondria, even though 3-hydroxykynurenine is synthesized in the outer mitochondrial membrane.

Topics: Amino Acids; Animals; Ascorbic Acid; Carboxylic Acids; Cytochromes; Kynurenine; Liver; Mitochondria, Liver; Oxazines; Oxygen Consumption; Pigments, Biological; Rats; Rats, Inbred Strains; Sodium Cyanide; Subcellular Fractions; Xanthenes