Protein L from the bacterial species Peptostreptoccus magnus binds specifically to the
variable domain of Ig light chains, without interfering with the antigen-binding site. In this
work a genetically engineered fragment of protein L, including four of the repeated Ig-
binding repeat units, was employed for the purification of Ig from various sources. Thus, IgG,
IgM, and IgA were purified from human and mouse serum in a single step using protein L-
Sepharose affinity chromatography. Moreover, human and mouse monoclonal IgG, IgM, and …