Protein antigens molecular weight

Now, while it is possible, by lowering the surface tension of the liquid medium to 50 dyn/cm by means of solutes of low molecular weight, to dissociate antigen-antibody precipitates (of the pure VDW type) (6), whole mammalian serum (with a surface tension < 50 dyn/cm) definitely has no such dissociating power. Upon some reflection this is not as anomalous as it might seem. Table I shows that it is mainly because of the presence of proteins (of molecular weight > 20,000) that blood (or plasma) has a surface tension y < 50 (and not y 70), and it cannot be expected that molecules with dimensions of the order of 100 A will effect a separation by purely physical means between other proteins of the same approximate size that are only about 2 A apart at their site of interaction (13). 

Radioimmunoassay (RIA) is a technique based on the formation of antigen-antibody complex. This technique essentially involves the application of isotope dilution analysis. An antigen is typically a protein of molecular weight greater than 10,000 that stimulates the production of antibody in an animal body. The antigen subsequently binds with the antibody. 

Figure 14.4. Diagram of three basic immunoassay formats, (a) Common competitive format (b) competitive assay with immobilized antigens bound to a carrier protein (immunometric assay) (c) two-site immunometric assays. Haptenic analytes are indicated as triangles, whereas larger-molecular-weight analytes are shown as teardrop shapes. Conjugated fluorescent probes are denoted by the letter "F. ...

---