ABSTRACT
Pectic esterases comprise enzymes that hydrolyze the esters present in the pectin backbone (EC 3.1.1.–). Currently three classes of esterases have been identified: (a) the pectin methylesterases (EC 3.1.1.11) that hydrolyze methylesters from O6 of galacturonic acid in the homogalacturonan part; (b) the pectin acetylesterases (EC 3.1.1.6); and (c) the rhamnogalacturonan acetylesterases (3.1.1.–). The acetylesterases remove acetyl groups from O2 and/or O3 of galacturonic acid residues either in the homogalacturonan part or in the rhamnogalacturonan part. Until now, no pectin methylesterase active toward methylesters in the rhamnogalacturonan part has been identified. The pectin methylesterases belong to family 8 of the carbohydrate esterase classification (1). The microbial rhamnogalacturonan and homogalacturonan acetylesterases have been grouped into family 12 whereas the plant pectin acetylesterases make up family 13 (1). Other esterases, like feruloylesterase, which are not active on the backbone but rather on side chains, will be covered elsewhere in this volume.
