Primary structure of human J chain: alignment of peptides from chemical and enzymic hydrolyses

Abstract

The primary structure of the J chain from a human Waldenstrom''s Ig[immunoglobulin]M protein was determined using a combination of automated and conventional Edman degradative procedures. Of the sequence, 85% was established with peptides isolated from tryptic digests of carboxyamidomethylated and citraconylated J chain, many of which were sequenced completely. Alignment of the tryptic fragments was achieved with peptides generated by chymotrypsin and limited acid hydrolyses. The J chain consists of 129 amino acids and a single oligosaccharide structure linked to asparagine at position 43 of the sequence. The MW, including 7.5% carbohydrate by wt, is 16,422. The location and arrangement of 3 half-cystines could be deduced from previous studies, whereas the pairing of the remaining 5 disulfide bonds still must be clarified.