2-chain immunoglobulin A molecules: abnormal or normal intermediates in synthesis.

Immunoglobulin A (gammaA) myeloma proteins secreted by plasma-cell tumors of mice are of two types, a common four-chain molecule and a rare two-chain (3.9S) molecule. The close similarity between two-chain gammaA molecules and four-chain gammaA molecules and their polymers is demonstrated in tryptic peptide maps of isolated polypeptide chains and by precipitin reactions with rabbit antiserums to gammaA immzunoglobulins. However, a difference between these two types is distinguishable with homologous antiserums. Homologous antiserums to two-chain gammaA immunoglobulins are specific and do not cross-react with four-chain gammaA immutnoglobulins.