IDENTIFICATION OF A LIPOXYGENASE INHIBITOR IN A431 CELLS AS A PHOSPHOLIPID HYDROPEROXIDE GLUTATHIONE-PEROXIDASE

An endogenous lipoxygenase inhibitor, purified from the cytosol of hum an epidermoid carcinoma A431 cells, was analyzed by N-terminal microse quencing and mass spectrometric analysis. The inhibitor was purified b y SDS-PAGE, then subjected to in-gel CNBr cleavage and trypsin digesti on. The N-terminal sequence data obtained from a 6-8 kDa band of in-ge l CNBr cleavage and the three isolated peptides of in-gel trypsin dige stion, and the C-terminal peptide sequence from matrix-assisted laser desorption ionization mass spectrometry matched the sequence of human phospholipid hydroperoxide glutathione peroxidase. The purified inhibi tor exhibited peroxidase activity using phosphatidylcholine hydroperox ides as the substrate. We therefore concluded that the lipoxygenase in hibitor present in A431 cells was a phospholipid hydroperoxide glutath ione peroxidase. (C) 1998 Federation of European Biochemical Societies .