Biochemical and Biosynthetic Studies of a Crystallizable Human γ1 Heavy‐Chain Disease Protein

Abstract
The structure of a crystallizable [human] .gamma.1 heavy-chain disease protein that lacks the entire VH [H chain, variable region] and C.GAMMA.1 [the 1st domain of the constant region of IgG] domains was studied. The protein starts within the hinge region at aspartic acid 221(Eu numbering). The native protein is disulfide-linked dimer with an apparent MW of 52,000, consistent with the biochemical data obtained on the whole protein and its cyanogen bromide fragments. The carbohydrate content of this protein was 6.8%. As shown by biosynthesis experiments intracytoplasmic .gamma. chains synthesized by neoplastic cells had an apparent MW similar to that of the serum H-chain disease protein. The data are compared with those obtained for other .gamma.1 H-chain disease proteins beginning in the hinge region, and the mechanisms leading to those abnormal Ig products are discussed.
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