β-Glucosidase multiplicity from Aspergillus tubingensis CBS 643.92:: purification and characterization of four β-glucosidases and their differentiation with respect to substrate specificity, glucose inhibition and acid tolerance

From Aspergillus tubingensis CBS 643.92 four distinct beta -glucosidases (I-IV) were purified by a four-step purification procedure. SDS-PAGE revealed molecular masses of 131, 126, 54 and 54 kDa, respectively, four distinct beta -glucosidases (I-IV) were purified by a four-step purification procedure. SDS-PAGE revealed and their isoelectric points were determined to be 4.2, 3.9, 3.7 and 3.6, respectively. The beta -glucosidases exhibited high diversity with respect to pH and temperature optima and stability, as well as to substrate specificity and glucose tolerance. The major beta -glucosidase (I) preferentially hydrolysed oligosaccharides. The acid-stable and heat-tolerant beta -glucosidase II hydrolysed aryl and terpenyl beta -D-glucosides as well as 1-O-trans-cinnamoyl beta -D-glucoside. In contrast to beta -glucosidases I and II, the minor beta -glucosidases III and IV were found to be glucose-tolerant; inhibition constants of 470 and 600 mM, respectively, were determined.