Isolation and properties of a succinylated subunit of human thyroglobulin

A subunit of succinylated (40:1 molar ratio, succinic anhydride:lysine residues) human thyroglobulin (Tg) was prepared by gel filtration on 6% and 4% agarose. This subunit (S-8) had a sdegrees20, w of 7.6S, Ddegrees20, w of 2.96 x 10(7) and an equilibrium molecular weight of 165,000 after correction for bound succinic anhydride (SA). The S-8 component was suggested to be a quarter unit of intact Tg. The S-8 and intact Tg had nearly identical amino acid compositions with differences only in glutamic acid, glycine and proline. The iodine content of both components was similar. The succinylated S-8 subunit, as well as material which sedimented with a value of 2S or less, retained some but not all heteroantigenic and autoantigenic sites in immunodiffusion and inhibition of passive hemagglutination.