Dissociation of thyroglobulin to a 26,000-dalton protein by succinylation is not blocked by pretreating the glycoprotein with trinitrobenzenesulfonic acid (TNBS). Treatment of normal, human thyroglobulin with TNBS alone causes dissociation of the large glycoprotein into smaller peptides some of which have molecular weights as low as 10,000. 19S thyroglobulin prepared from a human endemic goiter is not dissociated by trinitrophenylation. Thus, the lysyl residues of thyroglobulin can be divided into two parts: the lysyl residues of 19S residual thyroglobulin and of the lO,OOO- dalton peptide react readily with TNBS but do not react with succinic analyaride. However, the lysyl residues of the 26,000 dalton peptide react readily with succinic anhydride and react poorly with TNBS.
