Localization of rat thyroid alkaline protease to mast cells.

Abstract

Studies on the cellular localization of the alkaline protease of the rat thyroid are reported. Three lines of evidence indicate that the enzyme is located in mast cells and is not present in acinar cells. The first is that treatment of rats with compound 48/80, a drug which degranulates mast cells, abolishes the proteolytic activity. The second is that histochemical staining with a specific substrate for the enzyme shows it to be present only in mast cells. The third is that there is sufficient activity present in the number of mast cells which exist in the thyroid to account for all the proteolytic activity detected. Since histochemical evidence indicates that thyroglobulin hydrolysis in vivo occurs in acinar cells, it is concluded that the alkaline protease which hydrolyzes thyroglobulin in thyroid homogenates cannot do so in vivo. (Endocrinology 78: 361, 1966)