Nonplasminogen-dependent protease in human plasma
JA Marcum and DL Kline
Equal volumes of plasma and 0.3 M K2HPO4, pH 7.4, were mixed, diluted
20-fold, and adjusted to pH 5.2. After incubation at 37 degrees C for 30
min, the euglobulin percipitate, redissolved in 0.1 M K2HPO4, pH 7.4,
developed caseinolytic activity (0.05 CTA U/ml). Na2HPO4 or NaCl of similar
ionic strength could replace K2HPO4. The pH optimum of the protease was
6.5, activity falling off sharply below pH 6.0 and above 7.4. The
proteolytic activity was inhibited by diisopropylphosphofluoridate and by
pancreatic trypsin inhibitor, but was not inhibited by soybean trypsin
inhibitor. The activity was not due to plasmin, contact activation, or
coagulation factors, since it was fully generated in plasminogen-depleted,
factors XII, XI, VII deficient, and prekallikrein-deficient plasmas.
Purified Cl-esterase was not caseinolytic in our system. Redissolved
euglobulin precipitate prepared from normal plasma without salt addition
could serve as starting material for the generation of caseinolytic
activity, as could serum, indicating that the Hageman factor cofactor and
thrombin are not required. The protease had no detectable procoagulant or
fibrinolytic activity.
Volume 54,
Issue 3,
pp. 607-613,
09/01/1979
Copyright © 1979 by The American Society of Hematology
