The end product of purine metabolism in human is uric acid. The sequence of reactions in purine nucleotides degradation is given below: Figure 11.6 Degradation of Purine Nucleotides
The synthesis of purine and pyrimidine deoxyribonucleotides occurs from ribonucleotides by a reduction of the C2 of ribose moiety as shown in Figure 11.5. This reaction is catalysed by a multi-subunit (two B1 and two B2 subunits) enzyme ribonucleotide reductase. The ribonucleotide reductase itself provides the hydrogen atoms needed for the reduction from its sulfhydryl groups. The reducing equivalents,…
The purine nucleotide synthesis is well coordinated to meet the cellular demands. The intracellular concentration of PRPP regulates purine synthesis to a large extent. This increase depends on the availability of ribose 5′-phosphate and the enzyme PRPP synthase. PRPP glutamyl amidotransferase is controlled by a feedback mechanism by purine nucleotides. That is, if AMP and…
Purine and their nucleosides may be converted directly to mononucleotides by salvage reactions. Conversion of purines and deoxyribonucleotides to mononucleotides is carried out by the so-called salvage pathway, which requires far less energy than the de novo synthesis. The most important step of the salvage pathway is phosphoribosylation by PRPP of a free purine to…
Ribonuclease and deoxyribonuclease, which are produced in the pancreatic juice, convert RNA and DNA primarily to oligonucleotides. This is further degraded to 3′- and 5′-mononucleotides by the enzyme pancreatic phosphodiesterase. A group of nucleotides degrade phosphate and release the bases before uptake (dietary purines and pyrimidines are not utilised for the synthesis of uric acid).…
Nucleotides consist of a nitrogenous base, a pentose and a phosphate. The pentose sugar is deoxyribonucleotides of DNA. The sugar is 2-deoxy D-ribose. Nucleotides participate in almost all the biochemical processes, either directly or indirectly. They are the structural components of nucleic acid (DNA and RNA) coenzymes involved in the regulation of several metabolic reactions.