Purification and characterization of beta-xylosidase activities from the yeast Arxula adeninivorans.

Abstract

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 sulphate polyacrylamide 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 Km values for p-nitrophenyl-beta-xylopyranoside were determined to be 0.23-0.33 mM. The beta-xylosidase activity was inhibited competitively by xylose. The deglycosylated enzymes were, however, stronger inhibited (Ki = 2.1 mM) as their glycosylated ones (Ki = 5.8 mM).