SELENIUM-DEPENDENT GLUTATHIONE PEROXIDASE-GI IS A MAJOR GLUTATHIONE-PEROXIDASE ACTIVITY IN THE MUCOSAL EPITHELIUM OF RODENT INTESTINE

Gpx2 mRNA, encoding a selenium-dependent glutathione peroxidase (GPX-G I), has been found to be highly expressed in the gastrointestinal trac t (GI) mucosal epithelium. In this study, we show that GPX-GI is produ ced in the mucosal epithelium of the adult rat GI tract and that the a ctivity levels are comparable to that from GPX-1. Post-mitochondrial s upernatant GPX activity from the mucosal epithelium of the complete le ngth of the small intestine was partially purified. A sample enriched for putative GPX-GI was fractionated by SDS-polyacrylamide gel electro phoresis. Polypeptides of 21 kDa and 22 kDa were digested with trypsin . After resolving the tryptic peptides by high pressure liquid chromat ography (HPLC), the major peaks were analyzed for their amino acid seq uence by Microflow-HPLC-Tandem Mass Spectrometry and automated Edman d egradation sequencing. Both methods revealed that the 21-kDa sample co ntained rat GPX-GI determined by the sequence homology with the deduce d mouse GPX-GI polypeptide sequence. Rat GPX-1 was also detected in th e samples. AntiGPX-GI and antiGPX-1 antibodies were used to determine the distribution of the respective isoenzyme activities along the leng th of the intestine and with respect to the crypt to villus axis in ra ts. GPX-GI and GPX-1 activities were uniformly distributed in the midd le and lower GI tract and with respect to the crypt to villus axis. GP X-GI activity accounted nearly the same percentage of the total GPX ac tivity as GPX-1 in all of the these compartments. Studies on the dista l ileum segment of wildtype and Gpx1 gene knockout mice showed that GP X-GI activity was also at parity with GPX-1 in the mucosal epithelium of this segment. (C) 1998 Elsevier Science B.V. All rights reserved.