Open Access
Review
Table 2
Overview of methods for NK activity determination
| Detection method | Measurement principle | Advantage | Shortcoming | Reference |
|---|---|---|---|---|
| Fibrinogen plate method | Thrombin hydrolyzes fibrinogen into fibrin, creating artificial thrombus plates composed of cross-linked fibrin. The enzymatic activity is linearly related to the logarithm of the area of the hyaline circle | Simple, intuitive, multiple samples can be measured simultaneously | The area of the dissolution circle is highly influenced by incubation time, and the resolution is low and susceptible to individual subjectivity | [97] |
| Fibrinogen block dissolution time method | NK reacts with fibrinogen, causing bubbles to rise to the surface, and the dissolution time is measured | Greater resolution, shorter measurement time | Multiple samples cannot be measured simultaneously, strict timing requirements | [98] |
| Casein-Folin-phenol method | Protease hydrolyzes casein to produce tyrosine (under alkaline conditions), which reacts with Folin's reagent to form a blue substance. The absorbance at 680 nm is measured to calculate enzyme activity | Simple, low-cost, can simultaneously measure multiple samples | Reaction time needs to be strictly controlled; large experimental error | [99] |
| Methylbenzene sulfonyl-L-arginine methyl ester (TAME) method | At 37 ℃, NK splits the substrate into methylbenzene sulfonyl-L-arginine and methanol. Formaldehyde is produced from methanol, which reacts with chromic acid to measure absorbance at 574 nm, positively correlating with NK activity | Simple operation, high sensitivity, short measurement time | Requires tight control of reaction time; reagents are susceptible to environmental influences | [100] |
| Ultraviolet spectrophotometry | NK reacts with fibrin to hydrolyze peptide bonds, causing a change in absorbance at UV 275 nm | Good precision and accuracy, short measurement time | Insufficient specificity, susceptible to interference from other substances | [101] |
| Tetrapeptide substrate method | The enzyme solution is incubated with the tetrapeptide substrate (Suc-Ala-Ala-Pro-Phe-pNA) at 37 ℃ for 1 min, and absorbance at 410 nm is measured per unit time | Simple method, high sensitivity, low cost | Limited ability to fully capture the fibrinolytic activity of thrombolytic agents | [98] |
| Enzyme-linked immunosorbent assay (ELISA) | Use a monoclonal antibody specific to NK, which binds specifically to NK and forms a complex with a polyclonal antibody attached to a marker enzyme. NK activity is measured via a peroxidase reaction | High sensitivity, anti-interference, and specificity | High operating costs, limited practical applications | [97] |
| Serum plate method | The absorbance at 655 nm is high when fibrin forms and decreases as NK dissolves the fibrin | Can measure multiple samples simultaneously, simple operation, and low cost | The preparation of artificial thrombi affects absorbance measurements | [102] |
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