Ceruloplasmin: Plasma Inhibitor of the Oxidative Inactivation of Alpha1-Protease Inhibitor1–3

When leukocyte lysosomal extracts are used as a source of elastase and are combined with a fraction of plasma containing sufficient alpha1-protease inhibitor (α1-Pi) to inhibit all but 30 to 40% of the elastase amidase activity, elastolysis occurs at 69% of the rate of the uninhibited elastase controls (0.125 M NaCl; pH, 6.5). Proteolysis of elastin requires the presence of NaCl. At pH 8.6, elastolysis is decreased to 30 to 40% of free elastase controls by 1.0 M NaCl. At pH 6.5, on the other hand, elastolysis is increased to 83% of the control values by these higher NaCI concentrations. The activity of human leukocyte myeloperoxidase is optimal at pH 6 to 6.5 and at NaCl concentrations between 0.25 and 1.0 M. Purified myeloperoxidase, α1 -Pi, and elastase, in the presence of NaCl and hydrogen peroxide, can reproduce this phenomenon at pH 6.5, suggesting that the occurrence of elastolysis in lysosomal extract-plasma mixtures may in part be a result of the oxidative inactivation of α1-Pi by myeloperoxidase ...