Fragmentation of human IgG by a new protease isolated from the basidiomycete Armillaria mellea.

Digestion of human IgG by a new lysine-specific protease, isolated from the basidiomycete Armillaria mellea, produced Fc and Fab fragments similar to those produced by papain digestion of the same molecule. Digestion appeared to be restricted to a single cleavage point within the hinge region of the IgG molecule. Myeloma proteins of IgG1, IgG3 and IgG4 subclasses were found to be digested at an extremely rapid rate whereas IgG2 myeloma proteins appeared to be resistant to digestion by this enzyme.