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Chain length effects of n-alkyl 1-oxygen- and n-alkyl 1-thio-beta-D-xylopyranosides on beta-D-xylosidases.

The effect of an homologous series of n-alkyl β-d-xylopyranosides (from methyl to octyl) and n-alkyl 1-thio-β-d-xylopyranosides (from methyl to hexyl) on the activity of β-d-xylosidases from different origins (Aspergillus niger, Aspergillus oryzae and Bacillus pumilus 12) was investigated. Hydrolysis of n-alkyl β-d-xylopyranosides (oxygen derivatives) was only measurable with the A. nigerβ-d-xylosidase, where maximal hydrolysis was observed with the n-butyl derivative. Furthermore the behaviour of the series of oxygen and sulfur derivatives was purely competitive with respect to the hydrolysis of p-nitrophenyl β-d-xylopyranoside by all of the three enzymes. The inhibition constants decreased with increasing chain length for both series and both fungal enzymes. For B. pumilus 12 such a relationship was only found for the thiocompounds, whereas for the oxygen series a pronounced maximal inhibition was observed for the n-butyl and n-pentyl derivatives. The contribution of hydrophobic regions at or near the active site is discussed and speculative interpretations are presented.