1, horseradish peroxidase mainly comes from vegetable plant horseradish, which is a complex of colorless glycoprotein and heme. HRP is the most widely used marker enzyme in enzyme-linked immunosorbent assay.

2. Alkaline phosphatase is a phosphohydrolase, which can be extracted from Escherichia coli or calf intestinal mucosa. P-nitrophenyl phosphate (p-NPP) is often used as the substrate of AP.

3. β -galactosidase (β-Gal) is derived from Escherichia coli, with a molecular weight of 540kD and an optimum pH of 6 ~ 8. Due to the lack of this enzyme in human blood, the enzyme label prepared with β -gal is not easily interfered by endogenous enzymes in the determination, thus improving the specificity and being used for homogeneous enzyme immunoassay.