Fungal glucuronoyl esterases and substrate uronic acid recognition.

Glucuronoyl esterases are enzymes involved in microbial plant cell-wall degradation. In this study we purified and characterized two recombinant Phanerochaete chrysosporium glucuronoyl esterases, PcGE1 and PcGE2. The catalytic activity of these and previously described glucuronoyl esterases was investigated on new synthetic substrates, methyl esters of uronic acids and their glycosides, prepared by esterification with ethereal diazomethane.The data obtained indicate that the enzymes hydrolyzed efficiently not only esters of 4-O-methyl-D-glucuronic acid, but also methyl esters of D-glucuronic acid carrying a 4-nitrophenyl aglycon. Moreover, the fact that they did not recognize the 4-epimers of these compounds, the D-galacturonic acid derivatives, supports the hypothesis that these carbohydrate esterases attack ester linkages between 4-O-methyl-D-glucuronic acid of glucuronoxylan and lignin alcohols.