Kininogenase activity of tonin

Tonin, known for its specific and direct generation of angiotensin II, was highly purified from rat submaxillary gland and investigated for kininogenase activity. For the substrate, heat-treated plasma from ox blood, and highly purified low-molecular-weight (LMW) and high-molecular-weight (HMW) kininogens, were used. The reaction product formed at pH 8.0 well satisfied the characteristics of kinin, i.e., depressor and oxytocic activities and reactivity with antibradykinin antiserum. Kinin formed by tonin from purified LMW kininogen was identified with bradykinin in high performance liquid chromatography and radioimmunoassay. The results revealed tonin's new capability of forming kinin in addition to the hitherto known pressor angiotensin II, indicating tonin, too, is a member of the "kinin- tensin enzyme system."