Protein A and Protein G have binding sites for the Fc portion of mammalian IgG. The capacity of these proteins for IgG varies with the species. In general, IgGs have a higher affinity for Protein G than for Protein A, and Protein G can bind IgG from a wider variety of species. The affinity of various IgG subclasses, especially from mouse and human, for Protein A varies more than for Protein G. Protein A can, therefore, be used to prepare isotypically pure IgG from some species. Protein L has an affinity for kappa light chains from various species. It can be used to purify monoclonal or polyclonal IgG, IgA, and IgM as well as Fab, F(ab′)2, and recombinant scFv fragments that contain kappa light chains. Note: Species such as bovine, goat, sheep, and horse whose Igs contain almost exclusively lambda chains will not bind well, if at all, to Protein L. This makes it suitable for isolating mouse monoclonal antibodies from cell culture supernatants without contamination by bovine IgG. See also Protein A, G, and L Detection Reagents.
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