Binding of n-alkyl beta-D-xylopyranosides and n-alkyl 1-thio-beta-D-xylopyranosides to beta-D-xylosidase from Bacillus pumilus PRL B12.

The binding of D-xylose and of a series of n-alkyl beta-D-xylopyranosides and their 1-thio analogues to beta-D-xylosidase from B. pumilus PRL B12 has been investigated. The binding constants and thermodynamic equilibrium parameters delta H0 and delta S0 have been determined. The enzyme does not distinguish between alpha- and beta-D-xylopyranose. Although the enthalpy of binding of D-xylose is very favourable, the overall free-energy is small, due to a large decrease in entropy. Furthermore, all of the evidence available suggests that the aglycon group is bound by unspecific, hydrophobic forces. However, simple correlations between the binding parameters and the relative hydrophobicity of the compounds could not be found. Unexpectedly, no parallelism between binding of n-alkyl beta-D-xylopyranosides and the corresponding 1-thio derivatives was found.