The salvage pathway is particularly important in certain tissues such as erythrocytes & brain where de novo (a new) synthesis of purine nucleotides is not operative. It is the main synthesis pathway of nucleotides. ... Aspartate and glutamine will provide the nitrogen. A defect in the enzyme HGPRT causes Lesch - Nyhan syndrome. As fundamental biomolecules, nucleosides play key roles in diverse cellular processes, ranging from cell signaling to metabolism ( 1 ). Thiopurine metabolites such as thioguanine nucleotides decrease the de novo synthesis of purine nucleotides by inhibiting amidotransferase enzymes and purine ribonucleotide interconversion and are incorporated into DNA and ribonucleic acid (RNA). The de novo synthesis of purine nucleotide means using phosphoribose , amino acids , one carbon units and CO 2 as raw materials to synthesize purine nucleotide from the beginning. This de novo synthesis creates opportunities for the preparation of diversity libraries and will support efforts in both drug discovery and development. CONTENTS. The metabolic requirements for the nucleotides and their cognate bases can be met by both dietary intake or synthesis de novo from low molecular weight precursors.Indeed, the ability to salvage nucleotides from sources within the body alleviates any significant nutritional requirement for nucleotides, thus the purine and pyrimidine bases are not required in the diet. Also, the cell is sensitive to the presence of any premade nucleotides in its environment and will down regulate their de novo synthesis pathways in favor of using what is already present in the surroundings. The de novo synthesis of purine nucleotides by which these precursors are incorporated into the purine ring proceeds by a 10-step pathway to the branch-point intermediate IMP, the nucleotide of the base hypoxanthine. AMP and GMP are subsequently synthesized from this intermediate via separate, two-step pathways. Synthesis of purine nucleotides differs fundamentally from that of pyrimidine nucleotides in that the bases are built on the ribose ring. De novo pathway and salvage pathway are two main pathways of synthesis of purine nucleotides. Bacteria are capable of interconverting purines (adenine and guanine) and interconverting pyrimidines (thymidine, cytidine and uracil). 1. Therefore, the de novo pathway is a major pathway while salvage pathway is a minor pathway. Nucleotides homeostasis depends on the three portion of pyrimidine metabolism: de novo synthesis, catabolism and recycling of these metabolites. De novo pathway acts as the main pathway while salvage pathway is important for purine nucleotide synthesis in the brain and bone marrow. De novo purine synthesis refers to the biochemical pathway that creates purine nucleotides from simple molecules. 24. 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