AN ASPERGILLUS-NIGER ESTERASE (FERULIC ACID ESTERASE-III) AND A RECOMBINANT PSEUDOMONAS-FLUORESCENS SUBSP CELLULOSA ESTERASE (XYLD) RELEASEA 5-5'-FERULIC DEHYDRODIMER (DIFERULIC ACID) FROM BARLEY AND WHEAT CELL-WALLS

Diferulate esters strengthen and cross-link primary plant cell walls a nd help to defend the plant from invading microbes, Phenolics also lim it the degradation of plant cell walls by saprophytic microbes and by anaerobic microorganisms in the rumen. We show that incubation of whea t and barley cell walls with ferulic acid esterase from Aspergillus ni ger (FAE-III) or Pseudomonas fluorescens (XylD), together with either xylanase I from Aspergillus niger, Trichoderma viride xylanase, or xyl anase from Pseudomonas fluorescens (XylA), leads to release of the fer ulate dimer 5-5'diFA E,E)-4,4'-dihydroxy-5,5'-dimethoxy-3,3'-bicinnami c acid]. Direct saponification of the cell walls without enzyme treatm ent released the following five identifiable ferulate dimers (in order of abundance): nyl]-2-methoxyphenoxy)-4-hydroxy-3-methoxycinnamic aci d, enyl)-7-methoxy-2,3-dihydrobenzofuran-3-carboxylic acid, 5-5'diFA, )-4,4'-dihydroxy-3,5'-dimethoxy-beta,3'-bicinnamic acid, and -6-methox y-1,2-dihydronaphthalene-2,3-dicarboxylic acid. Incubation of the whea t or barley cell walls with xylanase, followed by saponification of th e solubilized fraction, yielded 5-5'diFA and, in some cases, certain o f the above dimers, depending on the xylanase used. These experiments demonstrate that FAE-III and XYLD specifically release only esters of 5-5'diFA from either xylanase-treated or insoluble fractions of cell w alls, even though other esterified dimers were solubilized by preincub ation with xylanase, It is also concluded that the esterified dimer co ntent of the xylanase-solubilized fraction depends on the source of th e xylanase.