Enzyme Technology in the Utilizatin of Agricultural Wastes

摘要

In this project, the enzymatic hydrolysis of xylan is studied. Xylan, the major hemicellulose in cereal grains, is hydrolyzed by the xylanase family of enzymes to yield a group of xylooligosaccharides which in turn are hydrolyzed by beta-xylosidase to xylose and xylooligosaccharides of lower molecular weight. Xylose has large potential use as a precursor for the sweetener, xylitol. This study investigated the purification and characterization of beta-xylosidases, separation of members of the xylanase family, and the properties of one of them (beta-xylosidase). Experimental materials and methods describe the enzyme source (A. niger), substrates, assay of xylanase and beta-xylosidase, and protein determination. Beta-xylosidase was purified over 100-fold in approximately 25 percent yield. At least four members of the xylanase family were separated and partially purified. Results indicate that beta-xylosidase has an optimum hydrolysis pH of 3.75 and an activation energy at pH 4.0 between 30-70 degree C of 11.9 kcal/mole. One xylanase with a molecular weight over 20,000 has an activation energy of approximately 5.5 kcal/mole at pH4. Activation energy for decay at pH 4.8 was 78 kcal/mole.