[Inhibition of the autoxidation of polyunsaturated fatty acids by superoxide dismutase]

In this comprehensive approach, inhibition of autoxidation of PUFA by SOD or other enzymes has been studied. The systems used were: 1) in miscible media in which enzyme, substrat, and peroxidation products are soluble; 2) in non-miscible media such as emulsions; 3) in heterogenous media containing subcellular fragments or whole blended tissue. Depending on experimental conditions, inhibition or activation of peroxidation by SOD can be observed in miscible systems. Other enzymes such as phospholipase A, xanthine oxidase, or horseradish peroxidase are protective in heterogeneous media. Moreover, PUFA hydroperoxide are scavenged by glutathione peroxidase which thus could lessen the autocatalytic effects encountered during peroxidation. Enzymatic inhibition of autoxidation in emulsions was not observed. We conclude that superoxide ion does not play a major role in the initiation of peroxidation and that it may very well act as a free radical chain terminator. In addition, other enzymes such as xanthine oxidase, horseradish peroxidase or phospholipase A show an effective although empirical protection against autoxidation in homogenates of tissues.