There are 4 purines and 4pyrimidines that are of concern to us.

Most intracellular purine bases are salvaged and pyrimidine salvage probably occurs.

Methionine andtryptophan are uniquely represented by a single codon.

We next investigated which metabolites were most concentrated in the EVs. In order to get an approximation of the intra-EV concentration range, we calculated the concentrations of the metabolites in the EVs by dividing the mole amount of metabolites with the total EV volumes in the samples (Table ). The total volume of EVs ranged between 60-830 nl within the uEV preparations and was 372 nl in the pEVs. These calculations indicated that the intra-EV concentrations of the metabolites varied from sub micromolar up to > 10 mM in both uEVs and pEVs (Table ). EVs from both sources were rich in D-Ribose 5-phosphate, the most abundant metabolite in pEVs and 3rd most abundant in uEVs, and other metabolites involved in nucleotide metabolism in mostly > 10 µM to mM range. Amino acid ornithine, with the highest concentration of metabolites in the uEVs and 15th highest in pEVs, and several other members of the urea cycle were present in > 50 µM to mM concentrations in the EVs. Ornithine serves also as a precursor for the biosynthesis of spermidine, a multifunctional polyamine that stabilizes nucleic acids and membranes, present in > 10 µM quantities in both EV types. In conclusion, our data indicated that the metabolite profiles of EVs from different sources contained similarities, but also distinct differences. The EVs carried a subset of metabolites from several pathways, with high intra-EV concentrations of some specific metabolites.

The detailed pathway of purine biosynthesis wasworked out primarily by Buchanan and G.

At the other extreme,leucine is represented by eight codons.

In this mannerthe limited array of twenty amino acids designated by the codons may beexpanded in a variety of ways to enable proper functioning of the resultingprotein.

In other words, ex­aminations of the translationprocess in the species that have been investigated have revealed that thecoding sig­nals for amino acids are always the same.


In the presence of 5,10-Methylenetetrahydrofolate and the enzyme thymidylate synthetase, the carbongroup is both transferred to the pyrimidine ring and further reduced to amethyl group.


Relatively low levels of nucleotides result indecreased inhibition of de novo synthesis, resulting in further overload of thenon-functioning salvage pathway and increased uric acid production.


Conversely, an accumulation of adenylateinhibits formation of adenylosuccinate by adenylosuccinate synthetase, withoutaffecting the biosynthesis of GMP.


We examine here the biosynthetic pathways of purine andpyrimidine nucleotides and their regulation, the formation of thedeoxynucleotides, and the degradation of purines and pyrimidines to uric acidand urea.

Pathway for Bifunctional purine biosynthesis protein PURH

First, there is evidence, especially in thede novo purine pathway, that the enzymes are present as large, multienzymecomplexes in the cell, a recurring theme in our discussion of metabolism.

Current concepts on the regulation of purine biosynthesis de novo ..

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

presented our views on how purine biosynthesis de novo is ..

The names of purine nucleosides end in -osineand the names of pyrimidine nucleosides end in -idine. Theconvention is to number the ring atoms of the base normally and to use l', etc.