PURINE SALVAGE PATHWAY
Starting from what we know.
Nucleotides consist of nitrogenous base, a ribose, and a phosphate. They are the structural constituents of DNA and RNA.
There are two pathways for the synthesis of the purine nucleotides.
The De Novo synthesis pathway and, Salvage pathway.
The former is the main nucleotide synthesis pathway and the latter is important one in brain and bone marrow. The de novo synthesis of nucleotides means using phosphoribose, amino acids, carbon units, CO2, as raw materials to synthesise nucleotide from the beginning. On the other hand, as the word salvage is self-explanatory; many cells have the mechanisms to retrieve the purine bases and nucleosides to synthesise purine nucleotides. This is the salvage pathway. Let us understand the salvage pathway.
Adenine, hypoxanthine, guanine produced during the breakdown of high energy compounds like RNA, DNA, ATP are salvaged to produce AMP, IMP, GMP. Adenine phosphoribosyl transferase catalyses the formation of AMP from adenine. Hypoxanthine-guanine phosphoribosyl transferase (HGPRT) catalyses the formation of IMP, GMP from hypoxanthine and guanine respectively. Phosphoribosyl pyrophosphate (PRPP) is the donor of ribose 5-phosphate in the salvage pathway.
So, purine salvage pathway is just retrieving the purines to form nucleotides. Easy. The enzymes here catalyse the transfer of phosphoribosyl to purines to make a nucleotide and hence they are named accordingly.