Enzymatic synthesis of lignin: Purification to homogeneity of the three O-methyltransferases of tobacco and production of specific antibodies

Abstract

Three o-diphenol- O-methyltransferases (OMTs; EC 2.1.1.6) involved in the biosynthesis of lignin have been purified to homogeneity from tobacco leaves. Seven different fractionation steps which included (NH 4) 2 SO 4 precipitation, conventional low-pressure chromatography on Ultrogel AcA34 and DEAE-cellulose columns, high-performance liquid chromatography (HPLC) on three different supports (Mono Q, Mono P, and TSK G-3000 SW columns), and finally preparative electrophoresis were necessary. At each step of purification, the protein content of the enzymatic fractions was analyzed by electrophoresis on polyacrylamide gels under denaturing conditions. Purified OMT I appeared on sodium dodecyl sulfate-polyacrylamide gel as a doublet with electrophoretic mobilities corresponding to molecular weights of 38,500 ± 2000 and 39,500 ± 2000. The other two enzymes migrated as single but rather broad bands with molecular weights of 42,000 (OMT II) and 43,000 (OMT III). Polyclonal antibodies were raised in rabbits. The titers of antibodies were measured by an indirect enzyme-linked immunosorbent assay method, and their specificity was demonstrated by immunoblotting enzyme preparations at different stages of purification. Immunodetection of the three enzymes with a specific antiserum suggested serological relationships between the three OMTs of tobacco.