Correlation between structural characteristics and immunological properties of the terpolymer L‐glutamic acid⁶⁰‐L‐alanine³⁰‐L‐tyrosine

The structure of the terpolymer L‐glutamic acid⁶⁰‐L‐alanine³⁰‐L‐tyrosine¹⁰ (GAT) has been investigated. GAT appears very heterogeneous in size as determined by gel filtration on a Sephadex G‐1 00 column. A dramatic downward shift in the average molecular weight (m.w.) is observed after gel filtration under denaturing conditions (Sepharose 6B, 6 M guanidine hydrochloride or polyacrylamide gel electrophoresis containing 0.1 % sodium dodecyl sulfate). We conclude that under nondenaturing conditions, GAT is a multimeric structure; the dissociation of the structure is reversible. GAT was fractionated based on the size of the polypeptide chains under denaturing conditions. After removal of guanidine hydrochloride three fractions were obtained with ∼ 100 000 (GAT fraction I), 45 000 (GAT fraction II) and < 10 000 (GAT fraction III) m.w., respectively. The immunological properties of these three fractions have been compared with those of unfractionated GAT. Fraction II resembles unfractionated GAT, showing similar immunogenicity in responder mice and suppressive properties in nonre‐sponder animals. Fraction I is less immunogenic, otherwise it resembles unfractionated GAT. Fraction III is the most dissimilar of the three fractions investigated. It retains the suppressive activity of GAT but is unable to stimulate a specific antibody response in responder animals. GAT fraction III is not a general tolerogen and is specifically suppressive for nonresponder mice.