FORMATION OF ALBIZZIINE AND 2,3-DIAMINOPROPANOIC ACID FROM URACIL IN ALBIZIA SEEDLINGS

Albizziine (2-amino-3-ureidopropanoic acid) was identified as a major radioactive metabolite of [2-C-14] uracil in tissues and enzymic extra cts of seedlings of Albizia julibrissin. Consistent with the biogenesi s of albizziine via uracil catabolism was the observation that [2-C-14 ]uracil is incorporated into isobarbituric acid (2,4,5-trihydroxypyrim idine) by crude enzymic extracts and microsomal preparations of seedli ngs of A. julibrissin and Pisum sativum in a tetrahydropterin-dependen t hydroxylation of uracil. Substantial stimulations, more than 500% ab ove the control value with A. julibrissin, were seen on addition of 6- methyl-5,6,7,8-tetrahydropterin. That there is a direct precursor rela tionship between uracil and albizziine was confirmed by the specific i ncorporation of the C-14-label from [2-C-14]uracil into the ureido-car bonyl of albizziine. This is as would be expected for the ring opening of a dihydropyrimidine, catalysed by dihydropyrimidinase. As 5-aminou racil had previously been identified as a precursor of albizziine, it was concluded from the present work that the biogenetic sequence from uracil involves first, hydroxylation to isobarbituric acid, then amina tion to 5-aminouracil, followed by hydrogenation and ring-opening, to yield albizziine, from which 2,3-diaminopropanoic acid is formed by th e action of beta-ureidopropionase. The formation of albizziine and 2,3 -diaminopropanoic acid represents a further example of the interfacing of pyrimidine primary and secondary metabolism through uracil.