Estimate the number of antigenic determinants on a molecule of BSA:
The number of antigenic determinants on each antigen molecule can be estimated if it is assumed that at extreme antibody excess every antigenic determinant is covered by a separate antibody molecule. If the amount of antibody in the precipitate formed under these circumstances is calculated then the relative numbers of molecules of antibody and antigen can be calculated, i.e:
In hyperimmune serum the bulk of the antibody is IgG which has a MW of 150,000. BSA has a molecular weight of 68,000. The molar ratio of antibody to antigen at your lowest antigen concentration will therefore be an estimate of the number of determinants on the antigen:
Therefore, there are TWO antibody binding sites on the BSA molecule!
(Allowing for experimental error, since the nearest integer to 1.93 = 2)
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