Purification and properties of a mast cell protease.

A mast cell protease has been purified over 260-fold from rat thyroid homogenates. The purified enzyme hydrolyzes denatured thyroglobulin, denatured hemoglobin, and fibrinogen. It also rapidly hydrolyzes the ester substrates, benzoyltyrosine ethyl ester, benzoylphenylalanine ethyl ester, and acetyltyrosine ethyl ester. The pH optimum for thyroglobulin and benzoyltyrosine ethyl ester hydrolysis is 7.8. The enzyme is inhibited by diisopropyl fluorophosphate, diphenylcarbamyl chloride and L-(1-tosylamido-Z-phenyl)ethyl chloromethyl ketone. The inhibition by diphenylcarbamyl chloride is prevented by indole. The molecular weight of the protease, based on sucrose density gradient centrifugation, is 23,000. Thus, the purified enzyme resembles chymotrypsin A in many of its properties.