Inhibition of rat tissue kallikrein gene family members by rat kallikrein‐binding protein and α1‐proteinase inhibitor

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.