α-Tocopherol Inhibits Human Glutathione S-Transferase π

Abstract α-Tocopherol is the most important fat-soluble, chain-breaking antioxidant. It is known that interplay between different protective mechanisms occurs. GSTs can catalyze glutathione conjugation with various electrophiles, many of which are toxic. We studied the influence of α-tocopherol on the activity of the cytosolic π isoform of GST. α-Tocopherol inhibits glutathione S -transferase π in a concentration-dependent manner, with an IC 50 -value of 0.5 μM. At α-tocopherol additions above 3 μM there was no GST π activity left. α-Tocopherol lowered the V max values, but did not affect the K m for either CDNB or GSH. This indicates that the GST π enzyme is noncompetitively inhibited by α-tocopherol. An inhibition of GST π by α-tocopherol may have far-reaching implications for the application of vitamin E.