Studies on the Metabolism of Kynurenic Acid

In preceding reports from this laboratory, kyneurenic acid was shown to be degraded by cell-free extracts of Pseudomonas Jluorescens (ATCC 11299B) with the formation of L-glutamic acid, Dand L-alanine, and acetic acid as the major end products (2, 3). Subsequently, tracer experiments with kynurenic acid labeled with Cl4 at various positions demonstrated that the carbon skeleton of glutamic acid was derived directly from the benzene moiety of kynurenic acid and that the pyridine moiety also contributed to glutamic acid formation by a circuitous mechanism (4). The enzymes involved in this pathway have now been purified, and the intermediate products have been isolated and identified. Available evidence indicates the sequence of reactions shown in Fig. 1 as a pathway of kynurenic acid degradation in this microorganism (5, 6). The present communication is concerned with the details of the initial phase of this metabolic sequence: the formation of 7,8-dihydroxykynurenic acid from kynurenic acid.