tailieunhanh - Báo cáo khoa học: Characterization of c-tocopherol methyltransferases from Capsicum annuum L and Arabidopsis thaliana

Tocopherols are essential micronutrients in human and animal nutrition due to their function as lipophilic anti-oxidants. Theyare exclusively synthesizedbyphotosynthetic organisms including higher plants. Despite the attributed beneficial health effects and many industrial applications, research on the tocopherol biosynthetic pathway and its regulation inplants is still limited. In theworkpresentedhere we performed a detailed biochemical characterization of a c-tocopherol methyltransferase (c-TMT) from Arabidopsis thaliana and of ac-TMT purified from Capsicum annuum fruits,a tissue with high accumulation of tocopherols. . | Eur. J. Biochem. 270 84-92 2003 FEBS 2003 doi Characterization of c-tocopherol methyltransferases from Capsicum annuum L and Arabidopsis thaliana Maria Koch1 2 Rainer Lemke3 Klaus-Peter Heise2 and Hans-Peter Mock1 Institute of Plant Genetics and Crop Plant Research Gatersleben Germany 2Albrecht-von-Haller-Institut fur Pflanzenwissenschaften der Universitdt Gottingen Germany 3Sungene GmbH Co. KgaA Gatersleben Germany Tocopherols are essential micronutrients in human and animal nutrition due to their function as lipophilic antioxidants. They are exclusively synthesized by photosynthetic organisms including higher plants. Despite the attributed beneficial health effects and many industrial applications research on the tocopherol biosynthetic pathway and its regulation in plants is still limited. In the work presented here we performed a detailed biochemical characterization of a y-tocopherol methyltransferase y-TMT from Arabidopsis thaliana and of a y-TMT purified from Capsicum annuum fruits a tissue with high accumulation of tocopherols. The biochemical characteristics of both enzyme preparations were remarkably similar including substrate specificities. Both enzymes converted Ỗ- and y- into b- and a-tocopherol respectively but b-tocopherol was not accepted as a substrate pointing lo a specific methylation at the C 5 -position of the tocopherol aromatic head group. A kinetic analysis performed with the Arabidopsis enzyme was consistent with an iso-ordered bi-bi type reaction mechanism. Our results emphasize the role of y-TMT in regulating the spectrum of accumulated tocopherols in plants. Keywords Arabidopsis Capsicum y-tocopherol methyltransferase vitamin E. a-Tocopherol belongs to a family of lipid-soluble hydrocarbon compounds characterized by a chromanol ring with a phytyl side chain and summarized under the collective name Vitamin E. Putative biochemical functions of these compounds are the antioxidant properties as efficient .