SOME PROPERTIES OF A THERMOSTABLE BETA-XYLOSIDASE FROM RHODOTHERMUS-MARINUS

The extracellular beta-xylosidase (EC 3.2.1.37) excreted by the thermo philic eubacterium Rhodothermus marinus when grown on xylan has been i nvestigated. The enzyme has been partially purified by ultrafiltration and gel filtration, and some of its characteristics are presented. Rh odothermus marinus grew on xylan with mu max = 0.4 h(-1) and the beta- xylosidase activity was 50 nkat/mL after 24 h in a batch fermentation. The beta-xylosidase activity had a half-life of more than Ih at 90 de grees C and of 14 h at 85 degrees C. At 80 degrees C, 80% of the initi al activity remained after 24 h. The initial activity increased with i ncreasing temperature, showing maximal activity at 90 degrees C. The b eta-xylosidase had a pH-optimum of 6 and was stable in the range betwe en pH 5 and 9. At pH 10 and 11, 82 and 66%, respectively, of the initi al activity remained after 24 h when incubated at 65 degrees C. The mo lecular weight was estimated to be 169,000 dalton by gelfiltration.