Afrikander cattle congenital goitre--thyroglobulin-related polypeptides smaller than the half-molecule sub-units

Crude congenital goitres from cattle were enriched in iodoprotein content by gel chromatography. From this fraction thyroglobulin-like protein was isolated by affinity chromatography with antithyroglobulin IgG. The goitre thyroglobulin-like protein constituted only about 20% of the iodoprotein fraction. By analytical ultracentrifugation three boundaries were present with apparent sedimentation rates of 3S, 10,3S and 15,1S respectively. In sodium dodecylsulphate (SDS)-polyacrylamide gels only a small proportion of the reduced polypeptides of the goitre thyroglobulin-like protein co-migrated with the known half-molecules of normal thyroglobulin, while the major proportion migrated as a heterogeneous group with apparent molecular weights smaller than the half-molecules. Heavy membrane-bound polysomes were prepared from normal and goitre tissue and incubated in a reticulocyte lysate amino acid incorporating system. The translation products were isolated by specific immunoprecipitation together with carrier thyroglobulin. In SDS-polyacrylamide gels both translation products contained radioactive polypeptides which co-migrated with the half-molecules of normal thyroglobulin. The translation products obtained from the goitre polysomes, however, contained a large proportion of polypeptides which migrated faster than the half-molecule sub-units.