PROTEOLYSIS IN PHOSPHATE-PURIFIED THYROGLOBULIN12

Abstract

Phosphate-purified thyro-globulin retained a small but consistent proteolytic activity when incubated at 37 [degree]C by itself or with hemoglobin. The proteolysis was maximal in the range of pH 3-4 and was readily abolished by heat. Divalent metals, cysteine, and TSH failed to affect the hydrolysis. The proteolytic component was separable from thyroglobulin. Purification produced a greater yield of the proteinase activity against hemoglobin, but not against thyroglobulin. The results suggest an enzyme-substrate linkage necessary for proteinase action which is irreversibly ruptured during the separation of the enzyme from thyroglobulin. Because of the demonstration of large peptide fragments when thyroglobulin is incubated at 37[degree] C, it is also suggested that the primary action of proteinase is to hydrolyze thyroglobulln into smaller molecules which are subsequently acted on by the thyroid peptidases to eventually liberate thyroid hormones.