Characterization And Application Of The Xylanosome From Streptomyces Olivaceoviridis

Characterization and application of a novel, large xylanolytic complex (xylanosome) by Streptomyces olivaceoviridis E-86 is studied. The major conclusions are as follows:1. The results of fermentation experiment showd that, corncob xylan was the best inducer and tryptone was the best nitogen of xylanosome formation, the xylanosome was produced when the organism was grown for 5 d between pH 4.5-6.0 and at 27.5 to 35 ℃. And the molecular weight was approx. 1200 kDa as determined on 3.5-15% native gradient gel electrophoresis.2. The xylanosome was purified to homogeneity by ammonium sulfate precipitation and Sephacryl S-300 gel filtration chromatography. It was composed of at least 8 subunits with molecular weight ranged from 12 to 60 kDa. Hererosubunits of 47, 35, 32 and 23 kDa were observed to demonstrate xylanase acivities, while 30 kDa had CMCase activity from SDS-PAGE zymogram. According to the N-terminal sequence analyses, the 47 kDa and 23 kDa subunits were found to be FXYN and GXYN. According to SDS-PAGE of seven purified enzyme produced by different carbon and nitrogen, results showed that different carbon and nitrogen sources present in the media affected the xylanosomal subunit composition.3. The optimal temperature and pH for xylanase activity was 60℃ and pH 6.0, respectively. The xylanase activity was stable within pH 4.1-10.3, and was stable up to 60℃ at pH 6.0. The xylanosome was highly specific towards oat-spelt xylan, and the main hydrolysis products of birchwood, beechwood, oat-spelt wood and corncob xylan were xylotriose, xylobiose and xylose, and analysis of these products from wheat arabinoxylan degradation by xylanosome confirmed that the enzyme has endoxylanase and debranching activities, with xylotriose, xylobiose, xylose and arabinose as the main degradation products. At the same time, different carbon and nitrogen sources also affected the specific activity of purified xylanosome. The xylanosome had the capacity of binding insoluble-oat spelt xyaln, which was a good explaination of its high specific activity to insoluble xylan.4. In this study, we also studied the application of xylanosome. The results of baking experiment showed that, at 20 mg/kg xylanosome adittion, specific volume of bread was increased 38.8%, firmness of bread was lowered to 1/3 of its original volume, and bread staling rate was significantly reduced. On different water unextractable-arabinoxylan : water extractable-arabinoxylan ratios studied, xylanosome hydrolyzed WUAX faster than WEAX. Hence, this enzyme is effective in improving the bread quality. From time course of hydrolysis of corncob powder, we knew that 80 U/100 mL dosage was proper under this hydrolysis condition, and the hydrolysis rate was 12.52% at 24 h. The results indicate the xylanosome can hydrolate native corncob powder.