ENZYMIC 4-0-METHYLATION OF GLUCURONIC ACID LINKED TO GALACTOSE IN HEMICELLULOSE POLY-SACCHARIDES FROM PHASEOLUS AUREUS

A particulate enzyme preparation from mung bean shoots can transfer the 14C-labelled methyl groups from S-adenosyl-l-methionine to the glucuronic acid unit of polysaccharides present in the particles. The labelled polysaccharides can be partly extracted by ammonium oxalate solution and partly by dilute NaOH (hemicellulose B). On partial acid hydrolysis, both fractions give an uronic acid mixture consisting predominantly of MeGlcUA-Gal besides some MeGlcUA-Xyl and MeGlcUA. This indicates that the products of the transfer reaction consist mainly of polysaccharides in which 4-O-methylglucuronic acid is linked to galactose, presumably methylglucuronogalactans. It is concluded that the mode of biosynthesis of the 4-O-methyl-d-glucuronic acid unit by transfer of methyl groups to preformed polysaccharides is the same regardless of the type of polysaccharide to which the glucuronic acid is linked. © 1969.