Production of substrate for galactose oxidase by depolymerization of an arabinogalactan-peptide from wheat flour

Water extractable arabinogalactan-peptide (WE-AGP) isolated from white wheat flour was depolymerized enzymatically to liberate substrate for a galactose oxidase from Dactylium dendroides. A crude liquid pectolytic preparation from Aspergillus niger (p70) displayed activities capable of converting WE-AGP into a substrate for galactose oxidase. The most favorable substrate was observed when WE-AGP was not fully depolymerized into galactose and arabinose, alpha-L-Arabinofuranosidase B from A. niger was also able to produce substrate from WE-AGP; arabinofuranosidase-treated WE-AGP was a better substrate for galactose oxidase than galactose. Treatment by the crude p70 and purified enzymes showed that alpha-L-arabinofuranosidase was partly responsible for the production of substrate, whereas beta-galactosidase did not result in any substrate production or improve the effect of alpha-L-arabinofuranosidase. However, the positive effect of alpha-L-arabinofuranosidase was increased when p70 was added at the same level of arabinofuranosidase activity, suggesting that additional enzyme activities present in p70 were responsible for production of substrate for galactose oxidase.