Circulating autoantibodies to mammalian tissue kallikreins

Inhibition of rat tissue kallikrein gene family members by rat kallikrein-binding protein and alpha 1-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 alpha 1-proteinase inhibitor (alpha 1-PI). Both these serpins inhibited kallikreins rK2, rK7, rK8, rK9 and rK10 with association rate constants in the 10(3)-10(4) M-1.s-1 range, whereas only 'true' tissue kallikrein rK1 was not susceptible to alpha 1-PI. This results in slow inhibition of rK1 by plasma serpins, which could explain why this kallikrein is the only member of the gene family identified so far that induces a transient decrease in blood pressure when injected in minute amounts into the circulation.

Differential interactions of human kallikrein-binding protein and alpha 1-antitrypsin with human tissue kallikrein

The characteristics of a new kallikrein-binding protein in human serum and its activities were studied. Both the kallikrein-binding protein and alpha 1-antitrypsin form 92 kDa SDS-stable and heat-stable complexes with human tissue kallikrein. In non-SDS/PAGE, the mobility of these complexes differ. Complex-formation between kallikrein and the binding protein is inhibited by heparin, whereas that between kallikrein and alpha 1-antitrypsin is heparin-resistant. In normal or alpha 1-antitrypsin-deficient-serum, the amount of 92 kDa SDS-stable complex formed upon addition of kallikrein is not related to serum alpha 1-antitrypsin levels. The rate of complex-formation between kallikrein and the binding protein is 12 times higher than that between kallikrein and alpha 1-antitrypsin. Purified alpha 1-antitrypsin, which exhibits normal elastase binding, has a kallikrein-binding activity less than 5% of that of serum. Binding of tissue kallikrein in serum is not inhibited by increasing elastase concentrations, and elastase binding in serum is not inhibited by excess tissue kallikrein. A specific monoclonal antibody to human alpha 1-antitrypsin does not bind to either 92 kDa endogenous or exogenous kallikrein complexes isolated from human serum. The studies demonstrate a new tissue kallikrein-binding protein, distinct from alpha 1-antitrypsin, is present in human serum.