Kynureninase from Neurospora: Purification

As part of a study of kynurenine metabolism in Neurospora crassa, the enzyme, kynureninase, has been investigated. Evidence from studies with mycelial pads suggests that tryptophan gives rise to kynurenine, which may be degraded to anthranilic acid (1). Kynurenine is also oxidized to hydroxykynurenine, which is converted to hydroxyanthranilic acid (2). The similarity of these reactions, i.e. the formation of anthranilic and hydroxyanthranilic acids, suggests that one enzyme is active for both kynurenine and hydroxykynurenine. In order to establish the specificity of Neurospora kynureninase, the purification of the enzyme was undertaken. An enzyme has been found in mammals (3, 4) which is able to convert kynurenine and hydroxykynurenine to alanine and anthranilic acid and to alanine and hydroxyanthranilic acid, respectively (5). A partially purified bacterial kynureninase preparation has also been obtained, but data for its action on hydroxykynurenine as substrate are not available (6). Evidence will be presented that kynureninase from Neurospora is able to convert L-kynurenine, 3-hydroxy-L-kynurenine, and N’-formyl-L-kynurenine to alanine and anthranilic acid, 3-hydroxyanthranilic acid, and formylanthranilic acid, respectively. Pyridoxal phosphate acts as coenzyme and magnesium ions activate the reaction.