Congenital goitre in sheep: isolation of the iodoproteins which replace thyroglobulin.

Immunological and chromatographic studies of proteins from the congenital goitre of South Australian Merino sheep revealed that normal thyroglobulin is absent from the thyroid glands of these sheep. However, a thyroglobulin-immunoreactive iodoprotein was isolated by affinity chromatography on agarose gel to which antibody against thyroglobulin had been covalently bound. Sucrose-gradient ultracentrifugation indicated that this iodoprotein had a sedimentation coefficient of 8S and a molecular weight of approximately 175000. This iodoprotein is therefore about one quarter the size of normal thyroglobulin (19S; 660000) and is similar in size to the subunit of thyroglobulin (3-8S; 165000) although this has usually been described as non-iodinated except when derived by reductive fission. In addition the goitre extract contained iodoproteins which had the immunological properties of serum albumin and immunoglobulin G. Determination of the iodine and iodoamino acid content of the hydrolysed 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.