N-terminal sequences of equine and human immunoglobulin heavy chains

Abstract

N-terminal tetrapeptides from heavy chains of equine γGab- and γT-globulins, and of human γG and γA myeloma proteins and a γM macroglobulin, have been studied. The equine and human heavy chains lacked free α-amino-terminal groups. After mild alkaline hydrolysis, glutamic acid was identified as the terminal amino acid by reaction with dimethylaminonaphthalenesulfonyl chloride, tentatively identifying pyrrolid-2-one-5-carboxylic acid (PCA) as the unreactive terminal residue of each heavy chain. Peptides lacking a free α-amino group were isolated from subtilisin and pronase digests of the heavy chains. The sequences of heavy chain N-terminal tetrapeptides were determined by digestion with carboxypeptidase A and were: equine γGab-globulins, PCA-Val-Gln-Leu; equine γT-globulins, PCA-Val-Gln-Leu; human γM macroglobulin, PCA-Val-Thr-Leu; human γAl myeloma protein, PCA-Val-Gln-Leu; human γGl (Gm f+) myeloma protein, PCA-Val-Gln-Leu. No class-specific N-terminal sequences were apparent.