The immunochemistry of a linear polymer and a branched copolymer containing the sequence Glu-Lys-Ala-Gly

The antibody specificity to a randomly coiled polypeptide of known sequence, poly (glutamyllysyl-alanyl-glycine), and to a branched copolymer ▪ were studies in rabbits bo inhibition of homologous precipitin reactions. The reactions of both polymers with their homologous antisera were substantially inhibited by the tetrapeptide, Glu-Lys-Ala-Gly. Inhibition of the precipitation of the sequential polypeptide with its antiserum increased with the size of the oligomers, up to the tetramer, (Glu-Lys-Ala-Gly) 4. From ultracentrifugal and chromatographic studies of the reaction of this antibody with the oligomers as well as passive cutaneous anaphylaxis (PCA) studies in guinea-pigs, it was concluded that the tetramer, but not the trimer, possessed two antigenic determinants. Inhibition of the reaction of the branched copolymer with its antiserum on a molar basis was independent of the length of the oligomer. The immunodominant region of the branched copolymer appeared to include the amino terminus of the tetrapeptide. The immune response to the linear polymer, on the other hand, was consistent with the presence in the latter of internal determinants.