Carbohydrate esterases

Serine carbohydrate esterases and transacylases. The commonest reaction mechanism is the standard serine esterase /protease mechanism, demonstrated paradigmally for chymotrypsin, involving an acyl-enzyme intermediate. The enzyme nucleophile is a serine hydroxyl, which is hydrogen bonded the imidazole of a histidine residue, whose other nitrogen is hydrogen bonded to a buried, but ionised, aspartate residue (Figure 6.28),... 

Aspartic carbohydrate esterases. CE 8 contains only pectin methyl esterases, which demethylate methyl esters of a-(l- 4)-polygalacturonan. Two X-ray crystal structures - from the bacterial plant pathogen Erwinia chry-santhemi and from carrot (Daucus carota), have been solved.The enzyme... 

Figure 6.31 Urease-like mechanism for CE 9 carbohydrate esterases.

Esters of cellulose with interesting properties such as bioactivity and thermal and dissolution behavior can be obtained by esterification of cellulose with nitric acid in the presence of sulfuric acid, phosphoric acid, or acetic acid. Commercially important cellulose esters are cellulose acetate, cellulose acetate propionate, and cellulose acetate butyrate. Cellulose esters of aliphatic, aromatic, bulky, and functionalized carboxylic acids can be synthesized through the activation of free acids in situ with tosyl chloride, iV,iV -carbonyldiimidazole, and iminium chloride under homogeneous acylation with DMA/LiCl or DMSO/TBAF. A wide range of cellulose esters that vary in their DS, various substituent distributions, and several desirable properties can be obtained through these reactions. Recently, a number of enzymes that degrade cellulose esters have been reported. Some of them are acetyl esterases, carbohydrate esterase (CE) family 1, and esterases of the CE 5 [169-172] family. 

Industrial production of chitosan from chitin is usually carried out by high concentration of NaOH at high tanperatures. Alternatively, the conversion from chitin to chitosan can be achieved by chitin deacetylase (CDA, E.C.3.5.1.41). CDA is one of the monbers of the carbohydrate esterase... 

Feruloyl Esterases. Psychrophilic feruloyl esterases are employed in industry for biomass degradation, biotransformation, and isolation of ferulic acid derivatives useful as antioxidant, antimicrobial, and photoprotectant properties. For instance, one studied feruloyl esterase from the psychrophilic bacterium, P. haloplanktis TAG 125, is a family 1 carbohydrate esterase and displays significant activity toward pNP-acetate, a- and yS-naphthyl acetate, and 4-methylumbelliferyl p-trimethylammonio cinnamate chloride (a model substrate for determining ferulolyl esterase activity) (23). 

More than 300 proteins are currently classified in the CAZy database, including glycoside hydrolases (GHs), glicosyltransferases (GTs), polysaccharide lyases (PLs) and carbohydrate esterases (CEs). Usually, CAZymes present a modular structure, nearly 7% of the enzymes having at least one carbohydrate-binding module [13]. CBMs are also classified... 

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