Papain cleaves the immunoglobin molecule into:
Ans. (b) 1 Fc and 2 Fab Antibody Fragmentation The performances of ceain immunoassay procedures are enhanced by using antibody fragments, such as Fab and F(a13'),. Antibody fragmentation is accomplished using reducing agents and proteases that digest or cleave ceain poions of the immunoglobulin protein structure. Antibody fragments of primary interest are: Antigen-binding fragments such as Fab and b. Class-defining fragments such as Fc that do not bind antigen. Technique of antibody fragmentation Papain digestion: A nonspecific, thiol-endopeptidase defragment IgG molecules into three fragments of similar size: two Fab fragment and one Fc fragment. Pepsin digestion: A nonspecific endopeptidase produces one F(ab')2 fragment and numerous small peptides of the Fc poion. The resulting F(ab')2 fragment is composed of two disulfide-connected Fab units. Ficin digestion A thiol protease that can digest mouse monoclonal IgG1 into either F(ab')2 or Fab fragments, depending on the concentration of cysteine included. Types of antibody fragments F(ab')2 fragments: F(ab')2 (110,000 daltons) fragments contain two antigen-binding regions joined at the hinge through disulfides. This fragment is void of most, but not all, of the Fc region. Fab' fragments: Fab' (55,000 daltons) fragments can be formed by the reduction of F(ab')2 fragments. The Fab' fragment contains a free sulfhydryl group that may be alkylated or utilized in conjugation with an enzyme, toxin or other protein of interest. Fab' is derived from F(ab')2. Fab fragments: Fab (50,000 daltons) is a monovalent fragment that is produced from IgG and IgM, consisting of the VH, CH1 and VL, CL regions, linked by an intramolecular disulfide bond. Fv fragments: Fv (25,000 daltons) is the smallest fragment produced from IgG and IgM that contains a complete antigen-binding site. Fv fragments have the same binding propeies and similar three-dimensional binding characteristics as Fab. Fc fragments: Fc (50,000 daltons) fragments contain the CH2 and CH3 region and pa of the hinge region held together by one or more disulfides and noncovalent interactions. Fc and Fc5jt fragments are produced from fragmentation of IgG and IgM, respectively. The term Fc is derived from the ability of these antibody fragments to crystallize. The Fc fragment cannot bind antigen, but it is responsible for the effector functions of antibodies, such as complement fixation.
1 Fc and 1 Fab
1 Fc and 2 Fab
2 Fc and 1 Fab
2 Fc and 2 Fab