Abstract:
When Bacillus circulans B6 was grown in a medium containing xylan as a sole carbonsource, the bacterium produced multienzyme complex, xylanosome which composed ofxylanolytic enzymes as a main enzyme and cellulolytic enzymes. During cultivation,xylanosome was found to adhere on cell surface from early log phase to late stationary phase sothat the enzyme activity and protein content could not be detected in the culture medium.Xylanosome was isolated from early log phase cell by eluting with 2% triethylamine andshowed only one band on native-PAGE, with a high molecular mass of about 299,000 Dalton.After xylanosome was released from cells, multienzyme complex was dissociated. Thereweremany protein bands on SDS-PAGE and at least 16 xylanases and 9 carboxymethylcellulases onzymogr~.Isdated xylanosome could adsorb to cells, insoluble xylan and avice1. It was stable inbroad range of pH 4.0-9.0 and temperature at between 40-60 OC. It had a higher pH stabilitythan crude enzyme (pH 4.0-7.0). The optimum conditions for xylanase activity of isolatedxylanosome were pH 7.0 and 60 OC while optimum conditions for that of crude enzyme werepH 6.0 and 60 OC.Purification of xylan-binding xylanase, an enzyme subunit of xylanosome, wasconducted in only one step using an affinity adsorption-desorption on insoluble xylan. Themolecular mass of purified xylan-biding xylanase was estimated at 44,000 Dalton and onlyacted on xylan. The enzyme was stable at pH 5.0-6.0 and temperature of 40-50 OC. Theoptimum pH and temperature were 6.0 and 60 OC, respectively. The enzymatic hydrolysisproducts of xylan were a series of short-chain xylooligosaccharides, indicating that the enzymewas an endoxylanase. The xylan-binding endoxylanase was effective closely on both hydrolysisof insoluble xylan and soluble xylan due to its xylan-biding region which is important forhydrolysis of insoluble xylan. Moreover, relative rates of hydrolysis of insoluble oat spelt xylanand larch wood xylan by xylan-binding endoxylanase were 90% and 89% respectively, whencompared with crude enzyme indicating that xylan-binding endoxylanase was more effective onhy&olysis of oat spelt xylan (soft wood xylan) than larch wood xylan (hard wood xylan).