Pyrimidine Metabolism. The Bases. Pyrimidines: Pyrimidine Biosynthesis. Note: CAA = Carbamoyl Aspartate; DHOA = Dihydroorotate; OMP = Orotidine. Pyrimidine catabolism. Pyrimidines are ultimately catabolized (degraded) to CO2, H2O, and urea. Cytosine can be broken down to uracil, which can be further broken down to N-carbamoyl-β-alanine, and then to beta-alanine, CO2, and ammonia by beta-ureidopropionase.‎De novo biosynthesis of · ‎Pyrimidine catabolism. Pyrimidine metabolism - Reference pathway, Help. [ Pathway menu | Organism menu | Pathway entry | User data mapping ]. Reference pathway, Reference.


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Xanthine oxidase is present in significant concentration only in liver and intestine.

Pyrimidine metabolism

The pathway to the nucleosides, possibly to the free bases, is present in many tissues. Gouts and Hyperuricemia Both undissociated uric acid and the monosodium salt primary form in blood are only sparingly soluble.

Hyperuricemia is not always symptomatic, but, in certain individuals, something triggers the deposition of sodium urate crystals in joints and tissues. In addition to the extreme pain accompanying acute attacks, repeated attacks lead to destruction of tissues and severe arthritic-like malformations.

The term gout should be restricted to hyperuricemia pyrimidine metabolism the presence of these tophaceous deposits. In gouts caused by an overproduction of uric acid, the defects are in the control mechanisms governing the production of - not uric acid itself - but of the nucleotide precursors.

The only major control of urate production that we know so far is the pyrimidine metabolism of substrates nucleotides, nucleosides or free bases. One pyrimidine metabolism to the treatment of gout is the drug allopurinol, an isomer of hypoxanthine.

Allopurinol is a substrate for xanthine oxidase, but the product binds so tightly that the enzyme is now unable to oxidized its normal substrate. Uric acid production is diminished and xanthine and hypoxanthine levels in the pyrimidine metabolism rise.

Pyrimidine Synthesis Pathway: Synthesis of pyrimidine derivatives

These are more soluble than urate and are less likely to deposit as crystals in the joints. Another approach is to stimulate the secretion of urate in the urine. Summary In summary, all, except ring-methylated, purines are deaminated with the amino group contributing to the general ammonia pool and the rings oxidized to uric acid for excretion.

Since the purine ring is excreted intact, no energy benefit accrues to man from these carbons. Pyrimidine Catabolism In contrast to purines, pyrimidines undergo ring cleavage and the usual end products of catabolism are beta-amino acids plus pyrimidine metabolism and carbon dioxide.

Pyrimidines from nucleic acids or pyrimidine metabolism energy pool are acted upon by nucleotidases and pyrimidine nucleoside phosphorylase to yield the free bases.

  • KEGG PATHWAY: Pyrimidine metabolism - Reference pathway
  • Pyrimidine metabolism in microorganisms.
  • Purine and Pyrimidine Metabolism
  • Pyrimidine Metabolism
  • Pyrimidine Metabolism

The 4-amino group of both cytosine and 5-methyl cytosine is released as ammonia. Atoms 2 and 3 of both rings are released as ammonia and carbon dioxide. The rest of the ring is left as a beta-amino acid. Beta-amino isobutyrate pyrimidine metabolism thymine pyrimidine metabolism 5-methyl cytosine is largely excreted.

Pyrimidine Metabolism Disorders - Pediatrics - MSD Manual Professional Edition

Beta-alanine from cytosine or uracil may either be excreted or incorporated into pyrimidine metabolism brain and muscle dipeptides, carnosine his-beta-ala or anserine methyl his-beta-ala.

General Comments Purine and pyrimidine bases which are not degraded are recycled - i.

This recycling, however, is not sufficient to meet total body requirements and so some de novo synthesis is essential. There are definite tissue differences in the ability to carry out de novo synthesis. De novo pyrimidine metabolism of purines pyrimidine metabolism most active in liver.


Non-hepatic tissues generally have limited or even no de novo synthesis. Pyrimidine synthesis occurs in a pyrimidine metabolism of tissues.

Pyrimidine metabolism in microorganisms.

For purines, especially, non-hepatic tissues rely heavily on preformed bases - those salvaged from their own intracellular turnover supplemented by bases synthesized in the liver and delivered to tissues via the blood.

The bases generated by turnover in non-hepatic tissues are not readily degraded to uric acid in those tissues and, therefore, are available for salvage. The pyrimidine metabolism probably does less salvage but is very active in de novo synthesis - not so much for itself but to help pyrimidine metabolism the peripheral tissues.