Study on a Family of Cystine-Containing Fragments from the Variable Part of Pig Immunoglobulin k-Chains.

From the tryptic hydrolyzate of pig immunoglobulin &kappa-chains 6 cystine-containing fragments were isolated. Amino acids analysis showed that they contained 37-70 amino acid residues and were of a variable nature. There exists a linear relationship between the specific electrical charge of the fragment and the ionic strength of the buffer by which the fragment is eluted from a column of QAE-Sephadex. Fragments, the disulfide bond of which was split by oxidative sulfitolysis, were split by thermolysin and the hydrolyzates were compared by the method of peptide maps. All the maps of fragments tested contained the peptide Ile-ThrSerCysSSO3-Arg (where CysSSO3 = S-sulfo-cysteine) which represents the vicinity of the half-cystine 24 of pig κ-chains, as shown by us previously. The nature of the peptide maps indicates that the individual fragments originate in the same section of the primary structure of the N-terminal half of the κ-chains. Each of the isolated fragments was a mixture of variants with an identical specific charge but with some amino acid replacements. [ABSTRACT FROM AUTHOR]