<Original>Roles of Bamboo O-methyltransferase in the Lignin Biosynthesis

Abstract

Bamboo 0-methyltransferase (OMT) was purified 97-fold by ammonium sulfate fractionation, and chromatography on DEAE-cellulose, Sephadex G-200 and -100 columns and analyzed by polyacrylamide gel electrophoresis and isoelectric forcusing. Two methylation processes, i.e. caffeate to ferulate (FA) and 5-hydroxyferulate to sinapate (SA), were demonstrated to be catalyzed by the same enzyme in the lignin biosynthesis. Bamboo OMT catalyzed the methylation of caffeate, 5-hydroxyferulate, 3,4,5-trihydroxycinnamate, 5-hydroxyvanillin, protocatechuate, but no or little methylation of chlorogenate, isoferulate, m-, p-coumarate, 3,4-dihydroxyphenylacetate, 3,4-dihydroxymanderate, gallate, pyrocatechol, pyrocatechol phthalein, and d-catechin. Km values for caffeate and 5-hydroxyferulate were 5× 10^<-5> and 10^<-5> M, respectively, and the former methylation was competitively inhibited by the latter phenolic substrate. The enzyme was an acidic protein with pI 4.61 at 4℃, and showed optimal pH at 8.0 with half maximal activities at pH 8.6±0.2 and 6.4±0.2. The ratio SA/FA in Gramineae and allied species was ca. 1.0 which was smaller than that of common angiosperm OMTs. This paper will discuss two possible regulatory mechanisms in the lignin biosynthesis which might be finely controlled by the OMT.