[Rule of antibody structure: the primary structure of a human monoclonal IgA1-immunoglobulin (myeloma protein Tro), V. The arrangement of the tryptic peptides and a discussion of the complete primary structure of the H-chain (author's transl)].

This communication deals with the sequence work done with tryptic and chymotryptic peptides and some cyanogen bromide splitting products. With these peptides, and if necessary with their splitting peptides, the whole primary structure of the alpha1-H-chain of myeloma protein Tro is established. The position of the amides is determined by electrophoresis and digestion with aminopeptidase M. The alpha1-chain Tro comprises 475 amino acid residues. Because of its specific exchanges and deletions the variable part of alpha1-chain Tro belongs to subgroup III of variable parts of H-chains. The switch from the variable to the constant part occurs at position 119/120 and is analogous to other chains which have been sequenced up to now. The large number of cysteine residues in the alpha-chain which may influence the tertiary structure, especially in the hinge and the subsequent CH2-region, is noteworthy. Furthermore, myeloma protein Tro is compared with the other alpha1-chain Bur[5] sequenced in the meantime, and protein But[6], which is an IgA2 molecule of the allotype A2m(2).