An analysis of the extracellular xylanases and cellulases of Butyrivibrio fibrisolvens H17c

Abstract

The extracellular xylanase and cellulase components of Butyrivibrio fibrisolvens H17c were investigated. Two major peaks of enzyme activity were eluted by hydroxylapatite chromatography and designated complex A (C_A), having cellulase activity, and complex B (C_B) having predominantly xylanase activity but with some activity on carboxymethyl cellulose (CMC). C_B was further purified on a DE-52 column and subjected to gel filtration. The xylanase and CMCase activities eluted in a single peak with an apparent molecular mass greater than thyroglobulin (M_r 669 000). CMC xymograms of polyacrylamide gels electrophoresed under non-denaturing conditions indicated the presence of five bands with CMCase activity from C_A and eight from C_B. Xylan xymograms under the same conditions indicated the presence of four bands of activity in C_B. Under mild denaturing conditions the xylanase activity in C_B was found in 11 bands with molecular mass ranging from 45 to 180 and the CMCase activity in three bands with molecular mass ranging from 45 kDa to 60 kDa. This indicates that C_B exists as a multi-subunit protein aggregate of xylanases, some of which also have cellulase activity.