CONGENITAL GOITER IN SHEEP - ISOLATION OF IODOPROTEINS WHICH REPLACE THYROGLOBULIN

Immunological and chromatographic studies of proteins from the congenital goiter of South Australian Merino sheep revealed that normal thyroglobulin is absent from the thyroid glands of these sheep. A thyroglobulin-immunoreactive iodoprotein was isolated by affinity chromatography on agarose gel to which antibody against thyroglobulin was covalently bound. Sucrose-gradient ultracentrifugation indicated that this iodoprotein had a sedimentation coefficient of 8S and a MW .apprx. 175,000. This iodoprotein is about 1/4 the size of normal thyroglobulin (19S; 660,000) and is similar in size to the subunit of thyroglobulin (3-8S; 165,000) although this was usually described as non-iodinated except when derived by reductive fission. The goiter extract contained iodoproteins which had the immunological properties of serum albumin and immunoglobulin G. Determination of the iodine and iodoamino acid content of the hydrolyzed iodoproteins revealed that they contained iodothyronines which were able to contribute to the production of thyroid hormones although the total iodothyronine content of the goitrous gland was less than that of the normal sheep thyroid gland.