Phospholipid hydroperoxide glutathione peroxidase.

In acute inflammation the activated leukocytes generate cytotoxic oxygen free radicals. The role of these radical species in the cellular damage following an acute inflammatory reaction is well known. On the other hand the extent of the cellular damage must be dependent on both the rate of the free-radical generation and the scavenging capacity of the tissues. Among the enzymes acting in the inhibition of this damage, a key role seems to be played by the new selenoenzyme phospholipid hydroperoxide glutathione peroxidase. Indeed the reduction of membrane hydroperoxides constitutes a secondary line of defence against lipid peroxidation, preventing the decomposition of hydroperoxides leading to the formation of new radicals. This enzyme inhibits lipid peroxidation and is as active as glutathione peroxidase on phospholipid hydroperoxides, on which no previously known peroxidase is active. Its protective activity for biomembranes, and the kinetic analysis in the presence of detergents, suggest its interfacial character. The inhibition of lipid peroxidation in the membranes apparently requires this enzyme, along with glutathione and vitamin E, in order to reduce the rate of the initiation reactions. This synergism bears out the role of this enzyme in the multilevel defence system against free-radical damage in tissues.