Continuous antigenic sites

Any approach that could facilitate the localization of continuous antigenic sites would certainly diminish the overall effort required for complete Immunochemical characterization. 

Myoglobin has five antigenic sites, each comprising a conformational 1y distinct continuous surface region of the polypeptide chain, and are situated on (Site 1) residues 16-21 1 or... 

Figure 9> Structure of the synthetic Mb peptides that were first used to study effect of peptide size on antibody response to immunization by free peptides (site 5, peptides 145-153 143-153 and 132-153) and to generate specific tolerance to preselected antigenic sites of Mb (peptides 143-153 135-153. 132-153. and truncated 139-153) The continuous lines in truncated peptide 139-153 indicate the absence of Ala and Tyr residues at positions 144 and 151. The residue in parenthesis is not required as part of the antigenic site in all antisera (1).

ELISA assays may be competitive or noncompetitive. As the name imphes, in a competitive ELISA, enzyme-labeled antigen competes with free antigen (the analyte of interest) for a fixed and limited quantity of immobihzed antibody binding sites. After incubation, the microtiter plate (sohd support) is rinsed to remove all unbound species and the enzyme substrate is added in saturating concentration. The conversion of substrate to produce can be measured continuously (kinetic assay) or, more commonly. 

The conventional competitive or non-competitive assays do not allow continuous detection so that, for on-line measurements, the so-called displacement assays are usually applied. Typically, the antibody is immobilized onto a solid support and packed in a column, and the corresponding antigen is labeled. The antibody binding sites are saturated with labeled antigens and the sample, containing the free (unlabeled) analyte, is injected into the column, resulting in displacement of the bound labeled analyte, as the affinity of the antibody for the labeled analyte is usually much lower than its affinity for the unlabeled analyte. The displaced labeled analyte is eluted and detected at the outlet of the column and the measured signal is directly proportional to the analyte concentration in the sample. 

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