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ARS Home » Midwest Area » Madison, Wisconsin » U.S. Dairy Forage Research Center » Research » Publications at this Location » Publication #102718

Title: AN ESTERASE FROM ASPERGILLUS NIGER (FAEA) CAN BREAK PLANT CELL WALL CROSS-LINKS WITHOUT RELEASE OF FREE DIFERULATES

Author
item CARCIA-CONESA, MARIA-TERESA - IFR NORWICH UK
item KROON, PAUL - IFR NORWICH UK
item Ralph, John
item MELLON, FRED - IFR NORWICH UK
item COLQUHOUN, IAN - IFR NORWICH UK
item SAULNIER, LUC - INRA NANTES FRANCE
item WILLIAMSON, GARY - IFR NORWICH UK

Submitted to: Journal of the Science of Food and Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/24/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary: The complex polysaccharides of many foods (for human and animal use) are often tied up by cross-linking and become partially unavailable for energy. In grasses, grains, and some products like sugar beet, this cross-linking is by small molecules called diferulates. Enzymes which degrade polysaccharides are often unable to degrade the portions near these cross- links. A potent enzyme from a fungus has been evaluated for its ability to attack the cross-link and release the polysaccharides (along with the diferulates). This enzyme was particularly effective at attacking some types of cross-links, but could not always release the polysaccharides from both sides of the cross-link. That is, it could release the polysaccharide from one end, but could not always fully release the other polysaccharide that was cross-linked to it. Nevertheless, releasing the single connection still allows a separation of the polysaccharides so that they may be more easily degraded by other enzymes. An understanding of the basic mechanisms involved in breaking cross-linking forms a foundation for improving the utilization of food resources by improving the digestibility of the polysaccharide component.

Technical Abstract: A cinnamoyl esterase (FAEA) from Aspergillus niger releases ferulic acid and 5-5- and 8-O-4- dehydrodiferulic acids from plant cell walls. The breakage of one or both ester bonds from dehydrodimer cross-links between plant cell wall polymers is essential for optimal action of carbohydrases on these substrates, but it is not known if cinnamoyl esterases can break these cross-links by hydrolysing one of the ester linkages which would not release the free dimer. It is difficult to determine the mechanism of the reaction on complex substrates, so we have examined the catalytic properties of FAEA using a range of synthetic ethyl-esterified dehydrodimers (5-5-, 8-5-Benzofuran and 8-O-4-) and two 5-5-diferulate oligosaccharides. Our results show that FAEA from Aspergillus niger is highly specific for hydrolysis of 5-5- and 8-5-dehydrodiferulates. The hydrolysis of diferulates to free acids occurs in two discrete steps, one involving dissociation of a monoesterified intermediate which is negativel charged at the pH of the reaction. However, although FAEA was able to release monomers as products of reactions with all three forms of diesters, some monoesters are not substrates for the enzyme and therefore FAEA does not always form the free diferulic acid. These results suggest a key role for this esterase in the degradation of plant cell walls through cleavage of at least one ester bond from the diferulate cross-links which exist between wall polymers.