Biochemical characterization of serum thyroglobulin from patients with bone metastases from follicular carcinoma of the thyroid.

The biochemical properties of serum thyroglobulin obtained from six patients with follicular carcinoma of the thyroid and distant metastases to bone(s) have been studied. Since it is difficult to isolate sufficient thyroglobulin from serum samples, in vivo radioiodinated serum thyroglobulin obtained after radioiodine administration was used. In contrast to a sharp salting-out pattern observed with native thyroglobulin isolated from normal thyroid tissue, a broad salting-out curve was seen with metastatic serum thyroglobulin. The metastatic serum thyroglobulin eluted with low ionic strength from ion-exchange column. More than 95% of metastatic serum thyroglobulin could be bound to concanavalin-A sepharose and be eluted with 0.5 M alpha-methyl mannoside. The reactivity of metastatic serum thyroglobulin and native thyroglobulin towards concanavalin-A was comparable. Both types of thyroglobulins showed identical mobilities on sucrose linear density gradient centrifugation. The metastatic serum thyroglobulin from follicular carcinoma of the thyroid thus appears to be 19 S thyroglobulin with near normal concanavalin-A binding sugars but altered surface charges.