Pyrimidine degradation pathway

Since D-hydantoinase was identified as dihydropyrimidinase, it is proposed that D-amino acid production from DL-5-monosubstituted hydantoins involves the action of the series of enzymes involved in the pyrimidine degradation pathway. Based on this proposal, D-decarbamoylase was thought to be identical with P-ureidopropionase (EC 3.5.1.6) which functions in pyrimidine metabolism. 

Know the purine and pyrimidine degradation pathways and the attendant pathologies. 

Takahashi et al. [6] revealed that in Pseudomonas putida (= P. striata) BFO 12996 d-hydantoinase is identical with dihydropyrirnidinase (EC 3.5.2.2), which catalyzes the cyclic ureide-hydrolyzing step of the reductive degradation of pyrimidine bases (Fig. 4). The same results were obtained for other hydantoinases from Pseudomonas sp. [22,23], Com-amonas sp. [23], Bacillus sp. [9], Arthrobacter sp. [24], Agrobacterium sp. [22], and rat liver [25]. From these results, it is proposed that D-amino acid production from dl-5-monosubstituted hydantoins involves the action of the series of enzymes involved in the pyrimidine degradation pathway [24,26,27], However, this contenticm has remained moot because of a lack of systematic studies on the enzymes involved in these transformations [28]. 

For the regulation of metabolic pathways metabolites are often used which are a product of that pathway. The basic strategy for the regulation is exemplified in the mechanisms employed in the biosynthetic and degradation pathways of amino acids, purines, pyrimidines, as well as in glycolysis. In most cases a metabolite (or similar molecule) of the pathway is utilized as the effector for the activation or inhibition of enzymes in that pathway. 

Studies on isolated DNA and sugar model compounds have allowed the determination of the main OH-mediated degradation pathways to the 2-deoxyribose moiety. In addition, data are also available on the influence ofthe double-helix structure on the fate of purine and pyrimidine base radicals. 

Dihydropyrimidinases (EC 3.5.2.2) are involved in the reductive pathway of pyrimidine degradation, catalyzing the hydrolysis of 5,6-DHU and 5,6-dihydrothymine to the corresponding Namino adds. However, dihydropyrimidinases have been more commonly known as hydantoinases [32, 33], as this enzyme can be used in the production of optically pure amino acids starting from racemic mixtures of 5-monosubstituted hydantoins using the so-called hydantoinase process, ... 

Xanthopterin and isoxanthopterin in which the carbon atom at position 4 of the pteridine was labeled with were prepared by Korte and Barke-meyer 18) and in a brief communication they stated that S. faecalis R and certain yeasts had some capacity to convert these pteridines to folic acid or to degrade them to uracil 19). If the degradative pathway of pteridines to uracil were reversible this would represent a possible route of pteridine biosynthesis from a pyrimidine arising either via orotic acid or possibly from purines. 

Examination of the pyrazino[2,3-rf]pyrimidine structure of pteridines reveals two principal pathways for the synthesis of this ring system, namely fusion of a pyrazine ring to a pyrimidine derivative, and annelation of a pyrimidine ring to a suitably substituted pyrazine derivative (equation 76). Since pyrimidines are more easily accessible the former pathway is of major importance. Less important methods include degradations of more complex substances and ring transformations of structurally related bicyclic nitrogen heterocycles. 

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