Date of Award

1991

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

First Advisor

William A. Pryor

Abstract

The effect, in vitro, of water soluble components of the particulate phase of cigarette smoke on the elastase inhibitory capacity (EIC) of human alpha-1-proteinase inhibitor ($\alpha\sb1$PI) is studied. Basic features of aqueous cigarette tar extract-mediated damage to $\alpha\sb1$PI are presented, as are mechanistic studies addressing the identities of damaging species and the nature of damage to $\alpha\sb1$PI. Aqueous cigarette tar extract (ACT) causes a slow loss of EIC, and retains this $\alpha\sb1$ PI damaging ability for hours. The damage to $\alpha\sb1$PI by ACT is dependent on its hydrogen peroxide content. Hydroxyl radicals or hypervalent metal species in the homogeneous phase of ACT do not damage $\alpha\sb1$PI, which is compatible with their high reactivity and poor selectivity. Hydrogen peroxide accounts for the major portion of the damage to ACT-exposed $\alpha\sb1$PI, probably by direct oxidation of critical methionyl residues. Free methionine, but not methionine sulfoxide, protects against damage to $\alpha\sb1$PI by ACT. Also, ACT-exposed $\alpha\sb1$PI contains appreciable methionine sulfoxide. The $\alpha\sb1$PI exposed to ACT also undergoes non-oxidative modification to produce a more anionic protein, but such modification does not contribute to the loss of EIC. Hydrogen peroxide, at concentrations relevant to those produced in ACT, causes a comparable rate of loss of EIC and appreciable formation of methionine sulfoxide in $\alpha\sb1$PI. However, hydrogen peroxide does not reproduce the non-oxidative modifications of ACT-exposed $\alpha\sb1$PI. Although exposures of $\alpha\sb1$PI to catechol/hydroquinone shows some similarities to ACT, it is generally a poorer model compared to hydrogen peroxide. Sulfhydryls and ascorbate protect $\alpha\sb1$PI in ACT due to various factors, such as direct reaction with hydrogen peroxide. Chelators do not protect $\alpha\sb1$PI completely from ACT-mediated damage, despite many potential roles for metals in the damaging mechanism. The small protection that is afforded by the chelators is probably related only to the inhibition of production, or the degradation of, hydrogen peroxide.

Pages

206

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