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ImmunoglobulinG - IgG

Electron microscope studies reveal immunoglobulin G to be a Y-shaped molecule its molecular weight is about 150,000. The enzyme papain cleaves IgG into three active fragments, each of MW 50,000. Two of these fragments bind antigens and are called Fab (F for fragment and a for antigen binding). Each Fab has one antigen binding site. Thus the IgG molecule has two antigen binding sites which bind to antigens and form a precipitate with it .Each IgG molecule binds to two antigen molecules. The overall effect of the action of several IgG molecules is the formation of a lattice.