The protection by ascorbate and glutathione against microsomal lipid peroxidation is dependent on vitamin E

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Abstract
Lipid peroxidation of rat liver microsomal fractions was monitored by its low‐level chemilunminescence in preparations from controls and vitamin‐E‐deficient animals. Measurements were made (a) of the duration of the lag phase τ0 after initiation with NADPH/iron‐ADP and (b) of the slope of the chemiluminescence increase. In microsomes with normal vitamin E (α‐tocopherol) level the lag phase τ0 was substantially increased by ascorbate; in contrast, even an enhanced peroxidation was observed with ascorbate in vitamin‐E‐deficient microsomes. Therefore, the ascorbate‐mediated protection of microsomal membranes against lipid peroxidation is dependent on vitamin E in the membrane. In vitamin E deficiency the pro‐oxidant effect of ascorbate was abolished when glutathione (GSH) was present. Likewise, GSH does not prolong the lag phase τ0 in vitamin E deficiency. However, GSH (but not cysteine) exerts an antioxidant effect both in controls and in vitamin E deficiency by decreasing the slope of the chemiluminescence increase during lipid peroxidation. The involvement of GSH in an enzyme‐dependent mechanism is suggested.