83] Kynurenine aminotransferase from kidney supernatant

Abstract

This chapter provides an overview of the kynurenine aminotransferase from kidney supernatant. L-kynurenine: α-ketoglutarate aminotransferase (cyclizing) activity of rat kidney supernatant, an enzyme in tryptophan catabolism, copurifies with the activity of α-aminoadipate: α-ketoglutarate aminotransferase. The presence of aminoadipate (kynurenine) aminotransferase in kidney represents an enzyme associated with lysine catabolism rather than with tryptophan degradation. α-aminoadipate (kynurenine) aminotransferase also catalyzes aminotransfer of 3,5-diiodotyrosine (halogenated tyrosine aminotransferase) suggesting a possible role in thyroid hormone metabolism. The reactions catalyzed by the kynurenine and halogenated tyrosine aminotransferase activities are presented diagrammatically. α-aminoadipate (kynurenine):α-ketoglutarate aminotransferase activity is also present in rat kidney mitochondria and the supernatant and mitochondrial fractions of rat liver. The activity of the L-α-aminoadipate aminotransferase is measured by the rate of disappearance or appearance of α-ketoglutarate with glutamate dehydrogenase. The chapter also reviews the kynurenine aminotransferase assay. The activity of kynurenine aminotransferase is measured spectrophotometrically by following the appearance of kynurenate.