Ureidoisobutyric acid

When the Tg lesions is opened by ammonolysis, the resulting product (snake venom phosphodiesterase, A exonuclease and the Klenow (exo ) fragment (Matray et al. 1995 see also Greenberg and Matray 1997). It is, however, removed by E. coli Fpg and Nth proteins (Jurado et al. 1998). 

Enzymatic synthesis of 3H-labelled P-ureidoisobutyric acid and P-aminoisobutyric acid from pHJthymidine... 

P-aminoisobutyric acid 59.3 pCi, p-ureidoisobutyric acid 18.8 pCi, radiochemical purity > 99% radiochemical purity > 99%... 

The synthesis of 14C-labelled / -ureidoisobutyric acid and / -aminoisobutyric acid from thymine using purified enzymes has been carried out earlier148. 

Figure 13-1 shows that reduction of the 5 6 double bond is the first step in the breakdown of the pyrimidine ring. This is followed by oxidative cleavage of the 3 4 bond to form ureidopropionic or ureidoisobutyric acid, from which /3-amino acids are formed with the release of NHj and CO. Whether carbamate or carbamyl phosphate is the primary product is not known. The /3-amino acids are then oxidatively deaminated to /3 dehydes, which are converted to acids which are variously metabolized. 

The cleavage of the reduced ring is a reversible reaction, sdelding -ureidopropionic acid in the case of dihydrouracil and jS-ureidoisobutyric acid in the case of dihydrothymine (X). ... 

Additional studies substantiated the I ole of dihydropyrimidines and 3-amino acids in pyrimidine catabolism. In the rat, thymine catabolism proceeded by reduction to dihydrothymine with the subsequent formation of j8-ureidoisobutyric acid (413, 4H) (Fig. 25). The fate of /3-aminoiso-butyric acid was uncertmn. 

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