beta-D-Xylosidase from the ruminal. anaerobic bacterium, Selenomonas ruminantium (SXA), catalyzes hydrolysis of beta-1,4-xylooligosacharides and has potential utility in saccharification processes. The enzyme, heterologously produced in Escherichia coli and purified to homogeneity, has an isoelectric point of approx 4.4, an intact N terminus, and a Stokes radius that defines a homotetramer. SXA denatures between pH 4.0 and 4.3 at 25 degrees C and between 50 and 60 degrees C at pH 5.3. Following heat or acid treatment, partially inactivated SXA exhibits lower k(cat) values, but similar K-m values as untreated SXA. D-Glucose and D-xylose protect SXA from inactivation at high temperature and low pH.