
<ArticleTitle>Inhibition of human <prot>glutathione S-transferase P1-1</prot> by tocopherols and alpha-tocopherol derivatives.</ArticleTitle>
<AbstractText>alpha-Tocopherol inhibits <prot>glutathione S-transferase P1-1</prot> (<prot>GST P1-1</prot>) (R.I.M. van Haaften, C.T.A. Evelo, G.R.M.M. Haenen, A. Bast, Biochem. Biophys. Res. Commun. 280 (2001)). In various cosmetic and dietary products alpha-tocopherol is added as a tocopherol ester. Therefore we have studied the effect of various tocopherol derivatives on <prot>GST P1-1</prot> activity. It was found that <prot>GST P1-1</prot> is inhibited, in a concentration dependent manner, by these compounds. Of the compounds tested, the tocopherols were the most potent inhibitors of <prot>GST P1-1</prot>; the concentration giving 50% inhibition (IC(50)) is &#60;1 microM. The esterified tocopherols and alpha-tocopherol quinone also inhibit the <prot>GST P1-1</prot> activity at a very low concentration: for most compounds the IC(50) was below 10 microM. RRR-alpha-Tocopherol acetate lowered the V(max) values, but did not affect the K(m) for either 1-chloro-2,4-dinitrobenzene or GSH. This indicates that the <prot>GST P1-1</prot> enzyme is non-competitively inhibited by RRR-alpha-tocopherol acetate. The potential implications of <prot>GST P1-1</prot> inhibition by tocopherol and alpha-tocopherol derivatives are discussed.</AbstractText>
