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What is the difference between F(ab) and F(ab’)2, and when would they be used?

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F(ab’)2 is a fragment of IgG that is prepared by pepsin digestion of IgG. F(ab’)2 fragment is the disulfide-linked heterodimer of the two light chain dimers, so it retains bivalent epitope binding like whole IgG, but because it lacks the heavy chains, it is smaller in size (~110 kDa compare to 150 kDa for whole IgG).

F(ab’) is a monovalent fragment consisting of a single light chain homodimer, which is obtained by pepsin digestion of IgG, followed by reduction of the light chain disulfide bond.

F(ab’)2 and F(ab’) fragments do not bind to immunoglobulin receptors on cells, which can be useful for achieving specific staining of the primary antibody target. The fragments also will not bind Protein A or Protein G.

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