PURIFICATION AND CHARACTERIZATION OF BETA-XYLOSIDASE ACTIVITIES FROM THE YEAST ARXULA-ADENINIVORANS

Beta-xylosidase activity has been detected in cell-free extracts, in culture fluids and as cell wall-bound enzyme of Arxula adeninivorans. With chromatographic procedures used to purify the activity two different forms of beta-xylosidase (denoted beta-X-1 and beta-X-2) from the cell-free extract and from the culture medium could be separated, but only one form (beta-X-2) was present in the cell wall. Both forms are glycoproteins and were deglycosylated by endoglycosidase H treatment. The molecular masses of the enzymes under native and denaturing conditions suggest that beta-X-2 is the dimer of beta-X-1. M(r) of the native beta-X-1 was 60 kDa and after deglycosylation 39 kDa determined by sodium dodecyl sulphatepolyacrylamide gel electrophoresis. Some enzymatic properties of beta-X-1 and beta-X-2 and of their deglycosylated products were studied and showed, with one exception, wide similarities. The maximum activity was reached at pH 5.0 and 60-degrees-C. The enzymes hydrolyze only beta-glycosidic bound beta-xylopyranosides and the K(m) values for p-nitrophenyl-beta-xylopyranoside were determined to be 0.23-0.33 mM. The beta-xylosidase acitivity was inhibited competitively by xylose. The deglycosylated enzymes were, however, stronger inhibited (K(i) = 2.1 mM) as their glycosylated ones (K(i) = 5.8 mM).