Biosynthetic And structural studies of a heavy chain disease protein

Abstract

A new heavy chain disease protein (_γHCD-JM) has been characterized by antigenic and structural criteria. The protein belongs to the IgG3-subclass and is closely related to Fc-fragment of G3-immunoglobulins. The predominant N-terminal amino acid of this protein is glutamic acid in the uncyclized form, and that of another _γHCD is glycine. Studies of the N-terminal peptides indicate that the N-terminal portion of the _γ3-heavy polypeptide chain is absent from the _γHCD-JM. These findings rule out a process of normal heavy chain initiation and a large deletion of the Fd region as being responsible for these two heavy chain disease proteins. The _γHCD-JM is a secretory product of cells from bone marrow as shown by studies of in vitro incorporation of amino acids-¹⁴C. Bone marrow and lymph node have a population of lymphoplasmacytic cells which by immunofluorescence contain _γ-heavy chain antigens in the absence of light chain antigens.