Microbial oxidation of kynurenic, xanthurenic and picolinic acids

Abstract

• 1.

  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.

  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.

  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.

  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.

  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.

  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.

  7. Evidence is presented that xanthurenic acid is not an intermediate in the conversion of kynurenic to 7,8-dihydroxykynurenic acid.

• 8.

  8. The Aerococcus and a Rhodotorula both attacked picolinic acid, and 6-hydroxypicolinic acid was isolated from arsenite-inhibited cultures.

• 9.

  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.