nitrogen metabolism (S)-allantoin degradation glyoxyldiureide degradation PMID:12460564 KEGG:map01100 anaerobic allantoin utilization KEGG:map01120 (2,5-dioxo-4-imidazolidinyl)urea degradation KEGG:map00230 5-ureidohydantoin degradation GO:0000256 UPa:UPA00395 PMID:16546208 pathway Anaerobic utilization of (S)-allantoin, a diureide of glyoxylic acid, as nitrogen source. ureide metabolism