The degradative pathway of the s-triazine melamine. The steps to ring cleavage

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Abstract
The degradative pathway of melamine (1,3,5-triazine-2,4,6-triamine) was examined in Pseudomonas sp. strain A. The bacterium grew with melamine, ammeline, ammelide, cyanuric acid or NH4+ as sole source of N, and each substrate was entirely metabolized. Utilization of ammeline, ammelide, cyanuric acid or NH4+ was concomitant with growth. But with melamine as substrate, a transient intermediate was detected, which was identified as ammeline by 3 methods. Enzymes from strain A were separated by chromatography on DEAE-cellulose, and 4 activities were examined. Melamine was converted stoichiometrically into equimolar amounts of ammeline and NH4+. Ammeline was converted stoichiometrically into equimolar amounts of ammelide and NH4+; ammelide was identified by 4 methods. Ammelide was converted stoichiometrically into equimolar amounts of cyanuric acid and NH4+; cyanuric acid was identified by 4 methods. Cyanuric acid was converted by an enzyme preparation into an unidentified product with negligible release of NH4+. The specific activities of the degradative enzymes (.gtoreq. 0.3 mkat/kg of protein) were high enough to explain the growth rate of the organism. The bacterium converted 0.4 mM melamine anaerobically into 2.3 mM NH4+. Two other pseudomonads and 2 strains of Klebsiella pneumoniae were also examined, with similar results. The degradative pathway of melamine appears to be hydrolytic, and proceeds by 3 successive deaminations to cyanuric acid, which is further metabolized.