Effect of granulocyte proteases on human coagulation factors IX and X. The protective effect of calcium.

: The inactivation of the zymogen and active forms of Factors IX and X by the effect of granulocyte proteases was investigated. As deduced from the apparent first-order inactivation rate constants, Factors IXa and Xa were about ten times as sensitive to proteolytic inactivation as the zymogen factors. In the presence of 2.5mM CaCl2 the rate of inactivation of zymogens decreased to one half. With the active factors, calcium caused complete resistance to proteolysis, prevailing for 15 min. The analysis of resistance to proteolysis, prevailing for 15 min. The analysis of resistance to proteolysis led us to the conclusion that the observed phenomenon was related to the calcium binding ability of the factors studied and can probably be explained by the protection of the active sites of enzymes.