Microbial oxidation of kynurenic, xanthurenic and picolinic acids

1. Resulta of a study of the degradation of kynurenic acid by an Aerococcus are in agreement with a reaction sequence proposed for Pseudomonas by other workers. This sequence includes Compounds I and II below. 2. Partial inhibition of oxidation of kynurenic acid by cell suspensions caused an accumulation of pyruvate with arsenite as inhibitor; α-ketoglutarate and aspartate accumulated when semicarbazide was used. 3. Crystals of Compound II, having properties expected for 5-β(carboxyethyl)-4,6-dihydroxypicolinic acid were isolated from cultures of the Aerococcus oxidizing kynurenic acid. 4. The properties are described of a solution of purified Compound I, also isolated from culture fluids. These properties are those expected for 5-(γ-carboxy, γ-oxopropenyl)-4,6-dihydroxypicolinic acid. 5. Dialysed cell-free extracts converted 7,8-dihydroxykynurenic acid to Compound I; the latter was degraded when reduced triphosphopyridine nucleotide was added to the extract. 6. Compound II was degraded by cell-free extracts; pyruvate, α-ketoglutarate, aspartate and glutamate were identified as reaction products; and when extracts were inhibited by semicarbazide the first of these compounds to appear were aspartate and α-ketoglutarate. 7. Evidence is presented that xanthurenic acid is not an intermediate in the conversion of kynurenic to 7,8-dihydroxykynurenic acid. 8. The Aerococcus and a Rhodotorula both attacked picolinic acid, and 6-hydroxypicolinic acid was isolated from arsenite-inhibited cultures. 9. Cell-free extracts of Rhodotorula converted picolinic to 6-hydroxypicolinic acid. The reaction can occur anaerobically in the presence of methylene blue and resembles the conversion of nicotinic acid to 6-hydroxynicotinic acid described by other workers for Pseudomonas.