Purification and characterization of a glutathione S-transferase Omega in pig: evidence for two distinct organ-specific transcripts

A cytosolic glutathione S-transferase (GST, EC 2.5.1.18) from the recently characterized Omega class [GSTO; Board et al. 2000, J. Biol. Chem. 275, 247 98-24806] has been identified in pig organs. It was found widely distribute d in the different tissues investigated and especially abundant in liver an d muscle. The hepatic enzyme has been purified to homogeneity by using its selective affinity for S-hexylglutathione over GSH, thus providing a simple method to isolate mammalian GSTO. The dimeric protein has a subunit molecu lar mass of 27328 Da as measured by electrospray ionization MS. Internal pe ptide sequencing and complete cDNA sequencing revealed strong similarities with its human recombinant orthologue and two rodent GST-like proteins with the ability to catalyse the GSH-dependent reduction of dehydroascorbate. A dditional similarities, including the presence of a specific N-terminal ext ension and of immunological cross-reactivity, support the results. Moreover . this gene encoding GSTO generates two organ-specific transcripts, suggest ing transcriptional mechanisms with a significance that is as yet uncharact erized.