Abstract
A particulate fraction from rat thyroid homogenates hydrolyzes thyroglobulin at a rapid rate. The pH range of activity is 7.0–10.0, and the maximum reaction rate occurs in 0.5–1.0M of various salts and 0.05M mercaptoethanol. The salt serves to solubilize the enzyme, and the mercaptan functions to reduce thyroglobulin nonenzymatically, thereby producing a better substrate for hydrolysis. The protease is in the cell fraction that sediments between 600 and 24,000 ×g. The products of hydrolysis of thyroglobulin range from free iodoamino acids to peptides of a molecular weight of 100,000. The yield of thyroxine, triiodothyronine and diiodotyrosine is increased by a heat labile supernatant factor, probably a peptidase. Although the enzyme actively hydrolyzes thyroglobulin in homogenates, it probably does not do so in vivo, as it is located in mast cells of the thyroid. (Endocrinology 78: 350, 1966)
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