Papain, immunoglobulin digestion

As depicted in Figure 50-8, digestion of an immunoglobulin by the enzyme papain produces two antigen-binding fragments (Fab) and one crystallizable fragment (Fc), which is responsible for functions of im-... 

IgG consists of four polypeptide subunits held together by disulphide bonds. Native immunoglobulins are rather resistant to proteolytic digestion but certain enzymes have been usefiil in elucidating their structure. Papain cleaves the molecule into three fragments of similar size ... 

Figure 32.3. The structure of the antibody molecule. All immunoglobulins consist of a basic subunit made up of four polypeptide chains (two light and two heavy) bound together by disulfide bonds. The variable region of the molecule contains the antigen binding site. Papain digestion yields a constant fragment (Fc) and variable fragments (Fab).

To escape the divalent character of immunoglobulin, Fab fragments which possess only one binding site can be used. Two different methods were described for purification of monovalent F.b fragments from IgG. One is a digestion by papain (Porter, 1959) at an enzyme-to-IgG final ratio of 1 25... 

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