The regulation of tissue kallikrein activity by plasma serine proteinase inhibitors (serpins) was investigated by measuring the association rate constants of six tissue-kallikrein family members isolated from the rat submandibular gland, with rat kallikrein-binding protein (rKBP) and α1-proteinase inhibitor (α1-PI). Both these serpins inhibited kallikreins rK2, rK7, rK8, rK9 and rK101 with association rate constants in the 103–104 M−1·s−1 range, whereas only ‘true’ tissue kallikrein rK1 was not suceptible to α1-PI. This results in slow inhibition of rK1 by plasma serpins, which could explain why this kallikrein is the ony member of the gene family identified so far that induces a transient decrease in blood pressure when injected in minute amounts into the circulation.
