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Abstract
Synthetic heterodisaccharides composed of glucose and xylose were tested as inducers of cellulose- and xylan-degrading enzymes in Aspergillus terreus, and the inducing abilities were compared with those of sophorose and xylobiose or their positional isomers. Measurement of secreted and cell-associated enzyme activities revealed that the heterodisaccharides induced the synthesis of the cellulolytic and xylanolytic enzymes, 2-O-?d-glucopyranosyl d-xylose (Glc?-2Xyl) being the most powerful inducer. Sophorose and 2-O-?d-xylopyranosyl d-xylose (Xy1/?-2Xy1), or their positional isomers, selectively induced the synthesis of cellulases and ?xylanases, respectively. An analysis of the extracellular enzymes (which were separated by isoelectric focusing followed by detection using chromogenic and fluorogenic substrates) showed that Glc?-2Xyl initiated the synthesis of specific endo-1,4-?glucanases and specific endo-1,4-?xylanases identical to those produced separately in response to sophorose or Xy1?-2Xy1. Glc?-2Xy1 also induced specific endo-1,4-?glucanases that hydrolysed 4-methylumbelliferyl ?lactoside at the agluconic bond. The results strengthen the concept of separate regulatory control of the synthesis of cellulases and ?xylanases. The results also suggest that mixed disaccharides, composed of glucose and xylose moieties, which may occur in nature, could play an important role in regulating the synthesis of wood-degrading enzymes.
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