PHGPX AND PHOSPHOLIPASE A(2)/GPX - COMPARATIVE IMPORTANCE ON THE REDUCTION OF HYDROPEROXIDES IN RAT-LIVER MITOCHONDRIA

The comparative importance of phospholipid hydroperoxide glutathione peroxidase (PHGPx) and of ''classic'' glutathione peroxidase (GPx) in the reduction of phospholipid hydroperoxides is unclear. Although GPx activity is 500-fold higher than that of PHGPx in rat liver,(1) the reduction of phospholipid hydroperoxides by glutathione (GSH) through GPx may be strongly limited by a low PLA2 activity. We address this issue using a moderately detailed kinetic model of mitochondrial lipid peroxidation in rat liver. The model was based on published data and was subjected to validation as reported in the references.' It is analysed by computer simulation and sensitivity analysis. Results suggest that in rat liver mitochondria PHGPx is responsible for almost all phospholipid hydroperoxide reduction. Under physiological conditions, the estimated flux of phospholipid hydroperoxides reduction through PHGPx is about four orders of magnitude higher than the estimated hydrolysis Aux through PLA2. On the other hand, virtually all hydrogen peroxide is reduced through GPx. Therefore, a functional complementarity between PHGPx and GPx is suggested. Because the results are qualitatively robust to changes of several orders of magnitude in PLA2 and PHGPx levels, the conclusions may not be limited to mitochondria.