The Major Fibrinolytic Proteases of Human Leukocytes

The major fibrinolytic enzymes present in leukocyte granules and active at physiological pH have been identified. The fibrinolytic activity in extracts of leukocyte granules was found to fibrinogen-Sepharose and eluted with 8.0 M urea. Two distinct zones of fibrinolytic activity were detected upon electrophoresis of leukocyte extracts on fibrinogen polyacrylamide gels, and both were qualitatively recovered in the 8.0 M urea eluate. Quantitatively, greater than 95% of the fibrinolytic activity was recovered in the urea eluate. Two major leukocyte proteases, elastase (EC 3.4.21.11) and cathepsin G (EC 3.4.21.-), were quantitatively recovered in the urea eluate. Both enzymes, when purified separately by affinity chromatography, were shown to: (a) possess fibrinolytic activity; (b) coincide in mobility and generate the two zones of fibrinolytic activity on fibrinogen polyacrylamide gels; and (c) quantitatively reconstitute the fibrinolytic activity of the leukocyte granules when combined at activity levels present in granular extracts. A highly significant correlation (r = 0.98) was found between the fibrinolytic activity and the sum of elastase and cathepsin G activity in leukocytes from five donors. Thus, elastase and cathepsin G are the major enzymes of the leukocyte fibrinolytic pathway, and fibrinogen-Sepharose chromatography may be used to obtain these enzymes.