The Effect of Catalase and Methionine-S-oxide Reductase on Oxidised α1-Proteinase Inhibitor

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Abstract
Oxidative damage to .alpha.1-proteinase inhibitor (.alpha.1-PI) may be important in the pathogenesis of emphysema. We have studied the ability of 2 enzymes (catalase and methionine-S-oxide reductase) to prevent and reverse oxidation of .alpha.1-PI by hydrogen peroxide. Pre-incubation of catalase with H2O2 protected .alpha.1-PI from oxidation, but the enzyme could not reverse prior oxidation of .alpha.1-PI. In contrast, methionine-S-oxide reductase fully restored activity to H2O2-oxidised .alpha.1-PI. Sputum sol-phase from smokers and non-smokers contained .alpha.1-PI that was only about 30% active. Functional activity increased in both smokers (p < 0.025) and non-smokers (p < 0.05) approximately 2-fold following incubation with the reductase. Western blotting of the samples showed that about 20% of the .alpha.1-PI was present as an enzyme-inhibitor complex and 20% was proteolytically cleaved. These observations suggest proteolysis, complexing with enzyme and oxidation are mechanisms of inactivation of .alpha.1-PI in lung secretions.

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