alpha-L-arabinofuranosidase from Ruminococcus albus 8: purification and possible role in hydrolysis of alfalfa cell wall

Abstract

An alpha-L- arabinofuranosidase has been purified from the extracellular broth of cultures of Ruminococcus albus 8. The purification procedure utilized gel filtration, (NH4)2SO4 precipitation, and isoelectric focusing. The purified enzyme appeared to be homogeneous when chromatographed on disc and analytical isoelectric focusing gels. The estimated molecular weight of the native protein was 305,000 to 310,000. Sodium dodecyl sulfate-gel electrophoresis analysis suggested that the native protein is a tetramer composed of 75,000-molecular-weight subunits. The enzyme appeared to have no metal cofactor requirement but was sensitive to several sulfhydryl reagents. The pH optimum with p-nitrophenyl-alpha-L-arabinofuranoside as the substrate was 6.9 and the Km was 1.3 mM. Several lines of evidence indicated that the enzyme is a glycoprotein. When assayed against alfalfa cell wall material, the enzyme hydrolyzed only small amounts of arabinose from the substrate. When assayed together with hemicellulolytic or pectinolytic enzymes against the same substrate, the arabinosidase significantly enhanced the hydrolytic action of the glycanases .