Comparative study of the peroxidase and iodinating enzyme of mouse thyroid and submaxillary gland

Abstract

1. 1. A comparative study on some aspects of the catalytic properties of peroxidase and iodinating enzymes of thyroid and submaxillary glands of the mouse has been made. 2. 2. Both the peroxidases are soluble and most of the activity is located in 105,000 g supernatant. However, the particulate fractions also show considerable activities. 3. 3. The iodinating enzyme of the thyroid gland is particle-bound, while that of the submaxillary gland is soluble in character. The 105,000 g supernatant of the thyroid gland cannot catalyse the iodination reaction even after dialysis. 4. 4. Both are true peroxidases, as evidenced by guaiacol peroxidation, however they differ in their relative ability to catalyse the oxidation of different electron donors such as o-dianisidine, guaiacol, and KI. 5. 5. The thyroid and submaxillary peroxidases differ in their optimum pH values and H₂O₂, requirements, the latter being markedly different for the oxidation of KI to I^3-. 6. 6. The iodinating enzymes of the thyroid and the submaxillary glands differ significantly with respect to their pH optima and their efficiency to catalyse the iodination of tyrosine or monoiodotyrosine. 7. 7. The submaxillary iodinating enzyme is unique in catalysing the "iodine exchange reaction", while the thyroid iodinating enzyme is incapable of catalysing the same.