Salvage synthesis

While the PRTases salvage nucleobases within cells, nucleosides such as adenosine and uridine are present in the blood at much higher concentrations ( 1 pM) than the equivalent nucleobases, adenine and uracil. Indeed, the brain synthesizes pyrimidine nucleotides (UTP and CTP) via salvage synthesis from uridine produced by the liver and released into the circulation. Human cells may contain at least three types of nonspecific nucleoside transporters, and nucleosides are internalized more rapidly than nucleobases. 

Enzymes that act on PRPP include Phosphoribosyltransferases (salvage synthesis and de novo synthesis of pyrimidines), PRPP amidotransferase... 

See also De Novo Biosynthesis of Purine Nucleotides, De Novo Pyrimidine Nucleotide Metabolism, Nucleotide Salvage Synthesis... 

AMP is also an intermediate in de novo synthesis of ATP (reaction 3 below) and salvage synthesis of ATP (reactions 4, 5, and 8 below). AMP is an allosteric activator of glycogen phosphorylase b, and phosphofructokinase, as well as an allosteric inhibitor of fructose-1,6-bisphosphatase and adenylosuccinate synthetase. AMP is also an allosteric inhibitor of glutamine synthetase, an enzyme with a central role in nitrogen metabolism in the cell. 

A similar reaction is catalyzed by adenylate kinase (see here also). The guanylate kinase-catalyzed reaction is part of de novo purine biosynthesis and can occur as part of purine salvage synthesis as well. 

UMP is a nucleotide intermediate in pyrimidine biosynthesis. It is produced by salvage synthesis and by the de novo pathway shown in Figure 22.10. 

Pyrimidine Nucleotide Metabolism, Nucleotide Salvage Synthesis... 

Salvage synthesis refers to the reuse of parts of nucleotides in resynthesizing new nucleotides. Salvage synthesis requires both breakdown and synthesis reactions in order to exchange the useful parts. 

Important enzymes in the salvage synthesis of nucleotides (Figure 22.2) are as follows ... 

Phospho-ot-D-ribosyl-l-pyrophosphate (PRPP) is an intermediate in both the de novo synthesis of nucleotides (Figure 22.1) and the salvage synthesis (reutilization) of nucleotides (Figure 22.2). 

Cytosolic thymidine kinase salvages exogenous thymidine extremely efficiently. Experiments with radiolabeled precursors show that dTTP derived from salvage synthesis is usually incorporated into DNA in preference to thymidine nucleotides generated by de novo synthesis. 

See also Nucleotide Analogs in Medicine, Nucleotide Salvage Synthesis, Salvage Routes to Deoxyribonucleotide Synthesis... 

See also The Importance of PRPP, De Novo Biosynthesis of Purine Nucleotides, Excessive Uric Acid in Purine Degradation, De Novo Pyrimidine Nucleotide Metabolism, Nucleotide Salvage Synthesis, Deoxyribonucleotide Biosynthesis, Biosynthesis of Thymine Deoxyribonucleotides, Salvage Routes to Deoxyribonucleotide Synthesis... 

Salvage Synthesis and Pyrimidine Catabolism (Figure 22.11) Deoxyribonucleotide Biosynthesis and Metabolism (Figure 22.12)... 

The main industrial method for the production of nucleotides is by enzymatic hydrolysis of yeast RNA to four nitrogenous bases with subsequent deamination of AMP to IMP, with CMP and UMP being waste products. Microbiological methods are being developed, based on the release of RNA derivatives, direct enzymatic production of nucleotides that are not RNA derivatives, and salvage synthesis (conversion of bases or nucleosides... 

Non- oxidative branch Pentose-5 -Phosphates Ribose-5-P 2 deoxy ribose-5-P 5 -phosphoribosyl-1 -pyrophosphate (PRPP) i) Structural components of nucleotides a. Basal structural component of RNA b. Basal structural component of DNA c. Precursor of both de novo and salvage synthesis of nucleotides ii) Intermediate products of purine metabolism and act as precursor molecules of cofactors, e g., riboflavin, flavin mononucleotide (FMN), flavin adenine di nucleotide (FAD) iii) Precursor of the amino acid. Histidine. 

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