Ureide biosynthesis

Unfortunately, allantoin breaks down to form allantoic acid under basic conditions such as those used for electrophoresis, and allantoin was not well separated from glutamine and other amino acids using this procedure. For these reasons, it has not been possible to ascertain whether allantoin was labeled, and, therefore, to distinguish between the two proposed pathways for ureide biosynthesis. 

Although the current popularity of the nucleic acids and their derivatives tends to focus attention first in that direction, other promising avenues of biosynthesis involving the glycosyl ureides have been suggested. Neuberg... 

Dihydroorotase (EC 3.5.2.3) is one of the known cyclic ureide-hydrolyzing enzymes, which catalyzes the reversible cyclization of L-ureidosuccinate to dihydro-Z/-orotate (Fig. 5c), the third step in pyrimidine biosynthesis. Dihydroorotase from P. putida IFO 12996 was purified to homogeneity and characterized [54]. The enzyme only hydrolyzed dihydro-L-orotate and its methyl ester, and the reactions were reversible. Dihydroorotase is specific for the siK-member cyclic ureides and shows the stereospecificity for the L-isomer. 

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