Figure 1.

De novo purine biosynthetic pathway. The de novo purine biosynthetic pathway uses six enzymes to catalyze the transformation of phosphoribosylpyrophosphate (PRPP) into inosine 5′-monophosphate (IMP) via 10 highly conserved step reactions. In the first step, pyrophosphate was replaced by the amino group of glutamine, and the imidazole ring was constructed on phosphoribosyl. After that, glycine, methylchuanyl and amino groups were connected in turn to form 5-aminoimidazole nucleotide (AIR). Then carboxylate to obtain the amino group of aspartic acid, formylate, and finally dehydrate to form IMP. When IMP gets amino group, it is converted into AMP. The amino group comes from aspartic acid, which forms adenylate succinic acid, and then splits to liberate fumaric acid (fumaric acid). The first reaction is catalyzed by adenylate succinate synthase (ADSS) and GTP provides energy. The second reaction is catalyzed by adenylate succinate lyase (ADSL). IMP can be oxidized by hypoxanthine nucleotide dehydrogenase (IMPDH) to produce xanthine, and then catalyzed by guanylate synthase (GMPs) to accept the amino group of glutamine to produce GMP. The remedial pathway of purine nucleotides mainly involves three enzymes: adenosine kinase (ADK), adenine phosphoribosyltransferase (APRT) and hypoxanthine guanine phosphoribosyltransferase (HGPRT). All three enzymes catalyze the production of NMP, but the substrate of ADK is adenosine, which consumes ATP; The substrate of the other two enzymes is the corresponding purine and PRPP is consumed.