Microbial metabolism of the pyridine ring. The hydroxylation of 4-hydroxypyridine to pyridine-3,4-diol (3,4-dihydroxypyridine) by 4-hydroxypyridine 3-hydroxylase

Abstract

1. The first metabolic step in the biodegradation of 4-hydroxypyridine by an Agrobacterium sp. was hydroxylation to form pyridine-3,4-diol. 2. Extracts required 1mol of O(2) and 1mol of NADH or NADPH for the conversion of 4-hydroxypyridine into pyridine-3,4-diol, suggesting that the enzyme responsible, 4-hydroxypyridine-3-hydroxylase, was a mixed function mono-oxygenase. 3. After treatment with acidic (NH(4))(2)SO(4) the enzyme required FAD for activity; FMN and riboflavin would not substitute for FAD. 4. The rate of anaerobic reduction of FAD by NAD(P)H was increased more than tenfold in the presence of 4-hydroxypyridine, suggesting that the mechanism of hydroxylation was similar to that of other aromatic hydroxylases which are of the mono-oxygenase type. 5. The partially purified enzyme was extremely specific for its heterocyclic substrate but would utilize either NADH or NADPH. 6. 4-Hydroxypyridine-3-hydroxylase was strongly inhibited by high substrate concentration (above 0.5mm) especially below pH7.5. 8. The inflexion at pH8.4 in a pK(m) versus pH plot, together with strong inhibition by p-chloromercuribenzoate, suggested a role for thiol groups in substrate binding.

Microbial degradation of pyridine by Paracoccus sp. isolated from contaminated soil

“…Since 1910s, researchers have isolated some microbial organisms degrading pyridine and its derivatives including hydroxypyridine, alkylpyridine and carboxypyridine, and elucidated microbial metabolic pathway of these compounds [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. There were some examples as following.…”

“…There were some examples as following. A group leaded by Cain [1,2,5,[9][10][11][12] from U.K. obtained some pure cultures with the ability to utilize pyridine as sole source of carbon, nitrogen and energy, and its hydroxy derivatives as principal carbon source by elective culture either from sewage of an activated-sludge plant or a few crumbs of soil. Five pure strains were selected for detailed study.…”

“…On the death and decay of the host species, these pyridine compounds are returned to the soil in the end. Nevertheless, when trace levels of these compounds were released into soils, they were rapidly degraded and even mineralized without contaminating the environment [1,2]. Coal gasification, retorting of oil shale and pesticide use have become anthropogenic sources of pyridine and its derivatives.…”

Enrichment and characterization of a bacterial culture that can degrade 4-aminopyridine

“…The biodegradability of pyridine derivatives follows the order pyridinecarboxylic acids > pyridine = monohydroxypyridines > methylpyridines > aminopyridines = chloropyridines [4]. Generally, pyridines are degraded via pyridine-ring reduction and fission steps [5] or via pyridine-ring hydroxylation and fission steps [6-8]. Nocardia sp.…”

“…In Agrobacterium sp. strain NCIB 10413, 4-hydroxypyridine is metabolized by a hydroxylase and an N -heterocyclic ring-cleavage dioxygenase [6,7]. Thus, the biodegradation of pyridines by single bacterial species has been studied, but little is known about the biodegradation of pyridines by microbial communities [10], which could include unculturable bacteria.…”