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The degradative pathway of the s-triazine melamine. The steps to ring cleavage
Abstract:
1. The degradative pathway of melamine (1,3,5-triazine-2,4,6-triamine) was examined in Pseudomonas sp. strain A. 2. The bacterium grew with melamine, ammeline, ammelide, cyanuric acid or NH+4 as sole source of nitrogen, and each substrate was entirely metabolized. Utilization of ammeline, ammelide, cyanuric acid or NH+4 was concomitant with growth. But with melamine as substrate, a transient intermediate was detected, which was identified as ammeline by three methods. 3. Enzymes from strain A were separated by chromatography on DEAE-cellulose, and four activities were examined. 4. Melamine was converted stoichiometrically into equimolar amounts of ammeline and NH+4. 5. Ammeline was converted stoichiometrically into equimolar amounts of ammelide and NH+4; ammelide was identified by four methods. 6. Ammelide was converted stoichiometrically into equimolar amounts of cyanuric acid and NH+4; cyanuric acid was identified by four methods. 7. Cyanuric acid was converted by an enzyme preparation into an unidentified product with negligible release of NH+4. 8. The specific activities of the degradative enzymes (greater than or equal to 0.3 mkat/kg of protein) were high enough to explain the growth rate of the organism. 9. The bacterium converted 0.4 mM-melamine anaerobically into 2.3 mM-NH+4. 10. Two other pseudomonads and two strains of Klebsiella pneumoniae were also examined, with similar results. 11. The degradative pathway of melamine appears to be hydrolytic, and proceeds by three successive deaminations to cyanuric acid, which is further metabolized.
Insights
Pseudomonas sp. strain A metabolizes melamine through a hydrolytic pathway. This bacterium converts melamine sequentially to ammeline, ammelide, and cyanuric acid, releasing ammonia at each step.
Area of Science:
- Microbiology
- Biochemistry
Background:
- Melamine is a nitrogen-rich compound with limited understanding of its microbial degradation pathways.
- Pseudomonas species are known for their metabolic versatility, suggesting potential roles in degrading xenobiotics like melamine.
Purpose of the Study:
- To elucidate the microbial degradation pathway of melamine in Pseudomonas sp. strain A.
- To identify the intermediate metabolites and enzymes involved in melamine breakdown.
Main Methods:
- Bacterial growth experiments using melamine and related compounds as sole nitrogen sources.
- Enzyme isolation and characterization using DEAE-cellulose chromatography.
- Identification of metabolites (ammeline, ammelide, cyanuric acid) using multiple analytical methods.
- Enzymatic assays to determine reaction stoichiometry and kinetics.
Main Results:
- Pseudomonas sp. strain A utilizes melamine, ammeline, ammelide, and cyanuric acid for growth, with melamine conversion yielding an intermediate identified as ammeline.
- Enzymatic studies confirmed a sequential hydrolytic deamination pathway: melamine → ammeline → ammelide → cyanuric acid, with ammonia release at each step.
- The identified enzymes exhibited sufficient activity to account for the observed bacterial growth rates.
Conclusions:
- The study establishes a detailed hydrolytic degradation pathway for melamine in Pseudomonas sp. strain A, involving three successive deaminations.
- This pathway leads to cyanuric acid, which is further metabolized by the bacterium.
- The findings contribute to understanding the biodegradation of nitrogen-containing heterocyclic compounds.