GLUTATHIONE S-TRANSFERASES OF RABBIT LUNG MACROPHAGES

The catalytic activities of glutathione S-transferases (GSTs), particu larly the alpha-class isozymes, can provide protection against oxidati ve stress through GSH-mediated metabolism of reactive products of lipi d peroxidation. Lipid peroxidation products from oxidative metabolism in alveolar macrophages play an important role in mediating and regula ting inflammatory response and injury in the lung. The rabbit has been used as an important animal model for studies of the role of alveolar macrophages in pulmonary pathology. Although rabbit lung macrophages display GST activity, the isozyme-specific expression of GSTs and the catalytic properties of these isozymes has not previously been defined . In present studies, we have purified the GST isozymes of rabbit alve olar macrophages obtained by bronchoalveolar lavage and performed immu nologic and kinetic characterization of the purified isozymes. Results of our studies indicate the presence of three alpha-class isozymes (p I 10.2, 9.3, and 6.0) and one mu-class isozyme (pI 7.2). N-terminal se quence analysis of the mu-class isozyme indicated that it was distinct from the two previously described mu-class isozymes of rabbit. Kineti c studies indicated that two cationic alpha-class GSTs (pI 10.2 and 9. 3) contribute the large majority of selenium independent GSH-peroxidas e activity toward dilinoleoyl phosphatidylcholine hydroperoxide (k(cat )K(m) values of 83.4 and 31.9 s(-1) . M-1 . 10(3), respectively). A th ird alpha-class GST (pI 6.0) was shown to have highest catalytic activ ity toward conjugation of the 4-hydroxynonenal (4HNE) with GSH (k(cat) K(m) = 1900 s(-1) . M-1 . 10(3)). Structural and immunologic character ization of this GST isozyme indicated that it belongs to a subclass of the alpha-class GSTs selectively expressed in mesodermal origin cells that are exposed to high levels of oxidative stress and are character ized by high specific activity toward both lipid hydroperoxides and 4- HNE. (C) 1998 Academic Press.