Natural substrates of human leukocyte elastase (ELP) in the blood are suspected to be fibrinogen and fibrin, although ELP is immediately complexed with α2-macroglobulin (α2M) and other inhibitors. However, the enzymatic activity of α2M·ELP complex is not yet clear. This study was undertaken to clarify the activity of the complex.
(1) ELP and α2M were purified respectively, then the α2M·ELP complex was prepared.
(2) The complex immediately after preparation degraded a specific synthetic substrate of ELP, Suc-Ala-Tyr-Leu-Val-pNA, independently of NaClO4 concentration in the reaction medium, different from the mode of action of free ELP.
(3) However, the complex could not degraded fibrin or fibrinogen without the addition of NaClO4.
(4) The amidolytic and fibrinolytic activities of the complex without addition of NaClO4 were 45% and 2% of those of free ELP, respectively, and those in the presence of 0.2M NaClO4 were 35% and 45%, respectively.
(5) After incubation at 37°C for over 24hr, the complex degraded fibrin and fibrinogen as well as synthetic substrate without the addition of NaClO4.
(6) The inhibition for amidolytic activity of the complex by various inhibitors was compared with those of ELP and pancreatic elastase (PE). The activity of the complex was not inhibited by various trypsin inhibitors and plasma inhibitors but was inhibited by Suc-Ala-Tyr-Leu-Val-CH2Cl and DFP.