title: A novel enzyme activity involving the demethylation of specific partially methylated oligogalacturonides.
abstract: Studies of the enzymic digestion of pectic substrates using different polygalacturonase (PG) preparations have revealed evidence for a previously unreported enzyme activity carried out by a contaminating enzyme in one of the preparations. This observed activity involves the demethylation of specific oligogalacturonides, namely 2-methyltrigalacturonic acid and 2,3-dimethyltetragalacturonic acid. However, no large-scale demethylation of highly methylated polymeric substrates is found, demonstrating that the enzyme responsible is not a conventional pectin methylesterase (PME). Furthermore, it has been shown that a commercial sample of fungal PME from Aspergillus niger demethylates all of the oligogalacturonides present as primary products of endo-PG digestion, in contrast with the activity observed here. On the basis of the known methyl ester distribution of the endo-PG-generated fragments and knowledge of which of these oligogalacturonides are demethylated, it is concluded that the observed activity can be explained by the existence of an exo-acting methylesterase that attacks the non-reducing end of the oligogalacturonide molecules.
authors.affiliation: Unilever R&D Colworth, Sharnbrook, Bedford, MK44 1LQ, U.K. bill.a.williams@unilever.com
authors.forename: Martin A K
authors.initials: MA
authors.lastname: Williams
authors.forename: Jacques A E
authors.initials: JA
authors.lastname: Benen
mesh_terms: D002265:Carboxylic Ester Hydrolases / Q000737:chemistry / Q000378:metabolism*; D019075:Electrophoresis, Capillary; D008745:Methylation; D009844:Oligosaccharides / Q000737:chemistry / Q000378:metabolism*; D010368:Pectins / Q000737:chemistry / Q000378:metabolism; D011096:Polygalacturonase / Q000737:chemistry / Q000378:metabolism*
chemical_list: D009844:Oligosaccharides; D010368:Pectins; D002265:Carboxylic Ester Hydrolases; C022323:pectinesterase; D011096:Polygalacturonase; C003181:polygalacturonic acid