A unique elastase in human blood platelets

Abstract

Previous investigations suggested that elastolytic activity found in platelets could be due to contamination by neutrophil elastase. In the present study, the lysate of blood platelets free of detectable neutrophils was examined for elastase-like activity using tertiary-butyloxycarbonyl (tBOC)-ala-ala-pro-ala-aminomethyl coumarin (I), tBOC-ala-ala-pro-val-aminomethyl coumarin (II), and succinyl-tri-ala-p-nitroanilide (SAPNA), and for elastolytic activity using 3H-labeled dog and human lung elastins. The platelet lysate degraded I at a higher rate than II, while the reverse was true of neutrophil elastase. The rate of degradation of I, II, and SAPNA by the lysate increased with reaction time up to 20 min. The rate of I, II, and SAPNA degradation by the lysate was decreased by the presence of 0.5 M NaCl, whereas NaCl greatly potentiated their degradation by neutrophil elastase. Plasma α2-macroglobulin inhibited elastolysis by the platelet lysate, whereas plasma α1-antitrypsin did not. The lysate activity was inhibited by diisopropyl fluorophosphate, phenylmethylsulfonyl fluoride, elastatinal, Trasylol, and furoyl-saccharin. The optimum pH for platelet lysate activity was 8.5-9.0, as in other studies using elastin as substrate. The pH 4.5 eluate obtained after incubation of the lysate with dog lung elastin at neutral pH exhibited the same catalytic properties as the activity in the lysate. The different substrate and inhibitor specificities and the failure of IgG specific for neutrophil elastase to remove elastase-like and elastolytic activities from the lysate indicate that a unique elastase occurs in platelets.