Splitting of human thyroglobulin. IV. The antigenicity of the pepsin-derived fragments.

Purified human thyroglobulin (Tg) was hydrolysed by pepsin. After completion of hydrolysis the pepsin hydrolysate was passed through a Sephadex G-200 column to remove undigested Tg. Further isolation of the enzymatic fragments was effected by passage through a Sephadex G-75 column. Two discrete fragments, termed pep I and pep II, were separated. The two fragments had sedimentation coefficients of 1-0 and 0-6, respectively. These fragments retained antigenic determinants reactive with both hetero-and auto-antibodies to Tg. The larger fragment, pep I, possessed all antigenic determinants to intact Tg while pep II lacked some determinants. Neither fragment contained novel determinants resulting from proteolytic degradation.