Jump to Synthesis - Pyrimidine is an aromatic heterocyclic organic compound similar to pyridine. One of the three diazines it has the nitrogen atoms at. Although both pyrimidines and purines are components in nucleic acids, they are made in different ways. Likewise, the products of pyrimidine degradation are. De Novo Synthesis of Pyrimidine Nucleotides. Since pyrimidine molecules are simpler than purines, so is their synthesis simpler but is still from readily available components. As is true with purine nucleotides, the sugar phosphate portion of the molecule is supplied by PRPP.


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Oxidation of the ring by a complex, poorly understood enzyme produces the free pyrimidine, orotic acid.

Pyrimidine Metabolism

This enzyme is located on the outer face of the inner mitochondrial membrane, in contrast to the other enzymes which are cytosolic. Note the contrast with pyrimidine synthesis synthesis in which a nucleotide is formed first while pyrimidines are first synthesized as the free base.

OMP is then converted sequentially - not in a branched pathway - pyrimidine synthesis the other pyrimidine nucleotides. Control The control of pyrimidine nucleotide synthesis in man is exerted primarily at the level of cytoplasmic CPS II. Other secondary sites of control also exist e.

These are probably not very important under normal circumstances. In bacteria, aspartate transcarbamylase is the pyrimidine synthesis enzyme.

There is only one carbamoyl phosphate synthetase in bacteria since they do not have mitochondria. Carbamoyl phosphate, thus, participates in a branched pathway in these organisms that leads to either pyrimidine synthesis nucleotides or arginine.


Interconversion of Nucleotides The monophosphates are the forms synthesized de pyrimidine synthesis although the triphosphates are the most commonly used forms. But, of course, the three forms are in equilibrium. There are several enzymes classified as nucleoside monophosphate kinases which catalyze the general reaction: Similarly, the diphosphates are converted to the triphosphates by nucleoside diphosphate kinase: One can legitimately speak of a pool of nucleotides in equilibrium with each other.

Salvaging of purine and pyrimidine bases is an exceedingly important process for most tissues. There are two distinct pathways possible for salvaging the bases.

Pyrimidine Metabolism

Salvaging Purines The more important of the pathways for salvaging purines uses enzymes called phosphoribosyltransferases PRT: As a salvage process though, pyrimidine synthesis are dealing with purines.

A-PRT is not very important because we generate very little adenine. Remember that the catabolism of adenine nucleotides and nucleosides is through inosine. This enzyme salvages guanine directly and adenine indirectly.

Lesch-Nyhan Syndrome HG-PRT is deficient in the disease called Lesch-Nyhan Syndrome, a severe neurological disorder whose most blatant clinical manifestation is an uncontrollable self-mutilation.

Lesch-Nyhan patients have very high blood uric acid levels because of an essentially uncontrolled de novo synthesis. It can be as much as 20 times the normal rate.

Pyrimidine - Wikipedia

Both of these factors could lead to an increase in the activity of the amidotransferase. Salvaging Pyrimidines A second type of salvage pathway involves two steps and is the major pathway for the pyrimidines, uracil pyrimidine synthesis thymine.

Formation of Deoxyribonucleotides De novo synthesis and most pyrimidine synthesis the salvage pathways involve the ribonucleotides. Exception is the small amount of salvage of thymine indicated above. Deoxyribonucleotides for DNA synthesis are formed from the ribonucleotide diphosphates in mammals and E.

A base diphosphate BDP is reduced at the 2' position of the ribose portion using the protein, pyrimidine synthesis and the enzyme nucleoside diphosphate reductase.