Antigenic and structural characteristics of an immunoglobulin-related peptide purified from marmoset T-lymphoma cells.

A 7800 Mr peptide, apparently derived from a 70,000 Mr immunoglobulin-related protein synthesized by a marmoset T-lymphoma cell line, bears immunoglobulin-related determinants apparently contained in a disulfide-bonded loop comparable to that of the VH fragment of classical H chain. A membrane-enriched, crude particulate fraction was prepared from marmoset T-lymphoma cells, and peptides generated by papain digestion of the particulate fraction were selectively purified by affinity chromatography using IgG purified from serum of a goat immunized with the Fab fragment of a human Waldenstrom macroglobulin. The smallest of the affinity-purified peptides was particularly reactive with unfractionated goat anti Fab (G alpha Fab) serum, purified IgG from G alpha Fab serum, and with antibodies affinity purified from G alpha Fab serum using Waldenstrom macroglobulins. Partial specificity of G alpha Fab antibodies was determined by competition radioimmunoassay and radioimmunoprecipitation assays. High-performance reverse-phase liquid chromatography was used for final purification of the smallest peptide which retained its reactivity with G alpha Fab serum and affinity-purified G alpha Fab antibodies. The apparent molecular weight of the peptide, determined by gel filtration in 6 M guanidine, was estimated at 3900 in its native state but increased to 7800 after reduction and alkylation, indicating a role for a disulfide bond in the tertiary structure of the peptide. The amino acid composition of the peptide was presented, and its possible relationship to immunoglobulin-like T-cell surface proteins was discussed.