Kynurenine-Transaminase, Kynureninase and the Increase of Xanthurenic Acid Excretion

Xanthurenic Acid Inhibits Metal Ion-Induced Lipid Peroxidation and Protects NADP-Isocitrate Dehydrogenase from Oxidative Inactivation.

“…Vitamin B6 deficiency further causes an increased excretion of xanthurenic acid, and the in creased xanthurenic acid level is an indicator of vitamin B6 deficiency (3). Many reports suggest that xan thurenic acid is closely related to the pathogenesis of several diseases (4)(5)(6), although the physiological role of this compound is unknown.…”

Kynurenine metabolism and xanthurenic acid formation in vitamin B6-deficient rat after tryptophan injection.

“…Holoenyzme activity of kynurenine aminotransferase in B6 -deficient kidney mitochondria was higher than that of cytosolic enzyme as reported peviously (2,29), and higher than that of B6-deficient liver mitochondria (17.2 -23.5nmol/min g of liver) (6). With regard to production of xanthurenic acid and kynurenic acid, therefore, B6-deficient kidney has favorable conditions compared with B6-deficient liver.…”

“…35, No. 2,1989 a Pyridoxal phosphate . Significances of differences between the values for the tryptophan-injected group and those for the non-injected group are denoted by *p<0 .05, **p<0.01, and ***p<0.001 (t-test).…”

“…ninase [EC 3.7.1.3 L-kynurenine hydrolase] increase the excretion of kynurenine, 3 -hydroxykynurenine, and xanthurenic acid into urine after tryptophan adminis tration (2)(3)(4)(5). We have previously shown that in B6-deficient rat kynurenine and 3 -hydroxykynurenine were heavily accumulated after tryptophan injection and there was a possibility of producing xanthurenic acid in liver in view of the Km values of kynurenine aminotransferase, and the activities of kynureninase were further decreased (6), probably by the xanthurenic acid accumulated (7).…”

The differences of the metabolism related to vitamin B6-dependent enzymes among vitamin B6-deficient germ-free and conventional rats.

“…It is known that aspartate and alanine aminotransferases are vitamin B6 dependent enzymes, and the determination of their enzymatic activities and the urinary excretion of xanthurenic acid are used as the criteria for the nutritional vitamin B6 status (1)(2)(3)(4). The mechanism of increased excretion of xanthurenic acid has been explained in view of the difference in the intracellular distribution of the related enzymes (5). It has also been reported that the presence of intestinal microflora may contribute something to the improvement of vitamin B6-deficiency in animals (6)(7)(8).…”