Purine nucleoside phosphorylase, abbreviated as PNP or PNPase, can reversibly catalyze the purine nucleoside phosphorylation reaction, causing the substrate purine nucleotide to decompose into corresponding purine and ribose-1-phosphate. It is an enzyme related to the synthesis and decomposition of nucleic acid DNA and RNA in the body. The monomers of DNA or RNA, namely nucleotides, are composed of a molecule of ribose or deoxyribose, a molecule of base and a molecule of phosphate. They are synthesized into double stranded or transcribed or reverse transcribed according to the principle of complementary base pairing (A-T, G-C), and translated into amino acid synthesis proteins according to different base sequences (codons). There are four types of bases, adenine A, guanine G, cytosine C, and thymine T (RNA corresponds to uracil U). Purine nucleoside phosphorylase is one of the key enzymes in the purine salvage synthesis pathway, widely present in prokaryotes and all fungal, animal, and plant cells. The specificity of purine nucleoside phosphorylase PNP varies from different sources. PNP in humans and higher animals and plants belongs to trimer, and can catalyze substrates such as adenine nucleotides and guanine nucleotides; The PNP of most bacteria is a hexamer, which can catalyze substrates such as adenosine and guanosine, as well as hypoxanthine nucleotides (inosine, which can serve as precursors for adenosine and guanosine); Some microorganisms have two types of polymer PNP present simultaneously. The detection principle of purine nucleoside phosphorylase activity: At pH 7.7 and a temperature of 37 ℃, 1 unit can oxidize 1 μ Mol's inosine phosphate generates hypoxanthine and ribose-1-phosphate. Enzyme committee number EC 5.4.2.2, CAS number 9030-21-1 or 9059-37-4. The enzyme has a molecular weight of 32kDa, an isoelectric point of 6.0, a Michaelis constant of 2.2X10-4M, an optimal pH value of 7.5-8.0 for enzyme activity, an optimal temperature of 60 degrees Celsius, a stable pH range of 5-10, and an inhibitor of silver ions and mercury ions. The detection related to PNP includes the application of Trinder reaction spectrophotometry to measure the activity of purine nucleoside phosphorylase (PNP) in red blood cells; PNP is coupled with xanthine oxidase uratase peroxidase, and serum 5 '- nucleotidase is measured using a dual reagent homogeneous rate method. Purine nucleoside phosphorylase can be used for multiple tests in biological research. Desheng's PNP is a reagent grade enzyme preparation, and the company's various Trinder's display reagents are used as biochemical reagent kits for enzymatic photometric detection.