Glutathione S-transferase (GST) isozymes of human lung have been purified, characterized, quantitated, and, based on their structural and immunological profiles, identified with their respective classes. The π-, μ-, and α-class GSTs represented 94, 3, and 3% activities of total human lung GSTs toward CDNB, respectively, and 60, 10, and 30% of total GST protein, respectively. Both the μ- and the α-class GSTs of human lung exhibited heterogeneity. The two μ-class GSTs of human lung had pI values of 6.5 and 6.25 and were differentially expressed in humans. Significant differences were seen between the kinetic properties of these two isozymes and also between the lung and liver μ-class GSTs. The α-class GST isozymes of lung resolved into three peaks during isoelectric focusing corresponding to pI values of 9.2, 8.95, and 8.8. All three α-class GSTs isozymes had blocked N-termini and were immunologically similar to human liver α-class GSTs. Peptide fingerprints generated by SV-8 protease digestion and CNBr cleavage indicated minor structural differences between the liver and the lung α-class GSTs. The three α-class GSTs of lung expressed glutathione peroxidase activities toward the hydroperoxides of phosphatidylcholine, phosphatidylethanolamine, and phosphatidylglycerol, with Km values in the range of 22 to 87 μm and Vmax values in the range of 67-120 mol/mol/ min, indicating the involvement of the α-class GSTs in the protection mechanisms against peroxidation. All three classes of lung GSTs expressed activities toward leukotriene A4 methyl ester and epoxy stearic acid but the μ-class GSTs had relatively higher activities toward these substrates.
ASJC Scopus subject areas
- Molecular Biology