THE PROTEOLYTIC ACTIVITY OF NORMAL AND PATHOLOGICAL HUMAN THYROID TISSUE1

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Abstract
THE importance of proteolytic enzyme systems in the synthesis of the thyroid hormone has been recognized since Salter and Pearson (25), using pepsin, were able to synthesize iodoproteins possessing activity similar to that of thyroglobulin. The same results were obtained by Salter and Lerman (24) with extracts of whole thyroid glands. These authors suggested the existence of an enzyme system which could either synthesize or hydrolyse the proteins according to the thermodynamic conditions. Gersh and Caspersson (7) suggested the possibility that enzymes in the thyroid gland hydrolyse thyroglobulin into polypeptides or peptones which could pass the cell membranes. In 1941 one of us (3) was able to demonstrate the existence of definite proteolytic activity in the colloid extracted by microdissection from a single follicle, and to establish a relation between this activity and the function of the thyroid gland. From these results, which were afterwards confirmed for the total gland by Dziemian (5), it was concluded that in the reabsorption of the follicular colloid an enzyme system may be involved, which is responsible for the hydrolysis of thyroglobulin and its breakdown into smaller molecules, and that the rate of this hydrolysis may depend upon the state of activity of the thyroid.