[Thyroid proteinase activity in toxic forms of goiter]

Shifts of the thyroid proteinase (cathepsin) activity in thyrotoxicosis were studied. It was found that both free and total activity of the thyroid lysosome cathepsins increase. The free activity, expressed as a percentage of the total one, is maximum in diffuse toxic goiter and is minimum in the healthy thyroid tissue. These differences in the thyroid cathepsin activity are due to destabilization of the lysosome membranes and their increased number in thyrotoxicosis according to the electron microscopy data. It is suggested that the thyroid lysosome cathepsins play a leading part in organic proteolysis, stipulating the thyroid hormone release.