Glucuronoyl esterases are active on the polymeric substrate methyl esterified glucuronoxylan

• Glucuronoxylan methyl ester serves as substrate of microbial glucuronoyl esterases.
• The enzymatic deesterification was monitored by 1H NMR spectroscopy.
• The signal of the ester group decreases while the signal of methanol increases.
• The substrate deesterification monitored by NMR can be used as activity assay.

Alkali extracted beechwood glucuronoxylan methyl ester prepared by esterification of 4-O-methyl-d-glucuronic acid side residues by methanol was found to serve as substrate of microbial glucuronoyl esterases from Ruminococcus flavefaciens, Schizophyllum commune and Trichoderma reesei. The enzymatic deesterification was monitored by 1H NMR spectroscopy and evaluated on the basis of the decrease of the signal of the ester methyl group and increase of the signal of methanol. The results show for the first time the action of enzymes on polymeric substrate, which imitates more closely the natural substrate in plant cell walls than the low molecular mass artificial substrates used up to present.