Splitting of human thyroglobulin. II. Enzymatic digestion.

The antigenic mosaic of human thyroglobulin was studied following proteolysis by papain, pepsin, trypsin and chymotrypsin. Undigested thyroglobulin (Tg) was removed from the enzyme-derived fragments by gel filtration. The fragments produced by the action of trypsin precipitated with rabbit heteroantibody to thyroglobulin but failed to precipitate when tested with human autoantibody to thyroglobulin. They only weakly inhibited the tanned cell haemagglutination reaction using either human or rabbit antiserum and failed to elicit antibody following injection with Freund's adjuvant into rabbits. The fragments produced by the proteolytic action of pepsin and papain differed from the trypsin product in that they precipitated with anti-normal human thyroid extract rabbit serum and (in the case of the pepsin fragment) human thyroiditis serum, and strongly inhibited the tanned cell haemagglutination reaction of either antiserum. They also elicited thyroglobulin-specific antisera in rabbits. Chymotrypsin-produced fragments failed to precipitate with, or to inhibit, either rabbit or human antisera. They were not immunogenic in rabbits.