The application notes include recommended starting dilutions; optimal dilutions/concentrations should be determined by the end user.
1/500 - 1/1000.
Protein L is a 36,000 dalton immunoglobulin-binding protein isolated from the bacteria Peptostreptococcus magnus. Unlike Protein A and Protein G, which bind to the Fc region of immunoglobulins (antibodies), Protein L binds antibodies through light chain interactions. Since no part of the heavy chain is involved in the binding interaction, Protein L binds a wider range of antibody classes than Protein A or G. Protein L binds to representatives of all antibody classes, including IgG, IgM, IgA, IgE and IgD. Single chain variable fragments (ScFv) and Fab fragments also bind to Protein L.
Despite this wide binding range, Protein L is not a universal antibody-binding protein. Protein L binding is restricted to those antibodies that contain kappa light chains and it is only effective in binding certain subtypes of kappa light chains - about 65% of human immunoglobulins carry kappa light chains.
Given these specific requirements for effective binding, the main application for immobilized Protein L is purification of monoclonal antibodies from ascites or cell culture supernatant that are known to have the kappa light chain. Protein L is extremely useful for purification of VLkappa-containing monoclonal antibodies from culture supernatant because it does not bind bovine immunoglobulins, which are often present in the media as a serum supplement. Also, Protein L does not interfere with the antigen-binding site of the antibody, making it useful for immunoprecipitation assays, even using IgM.