SUMMARY: Cellobiono-1,5-lactone (CBL) induces cellulase, particularly cellobiohydrolase I (CBH I) formation in When used as a sole source of carbon, it promoted comparably poor growth, because () the β-gluconolactone arising by the action of β-glucosidase is not metabolized by the fungus, and () it is a low- substrate of the β-glucosidase. Induction of higher amounts of CBH I were observed when CBL was supplied as carbon source together with cellobiose than when supplied alone. Maximal CBH I levels formed under these conditions were comparable to those when was grown on cellobiose plus β-gluconolactone, an inhibitor of β-glucosidase. These data suggest an indirect effect of CBL on CBH I induction, probably by inhibiting cellobiose hydrolysis. The origin of CBL during growth of on cellulose was also investigated: aldonic acids and aldonolactones were released from cellulose by culture fluids. Artificially oxidized celluloses gave rise to the appearance of higher concentrations of oxidized products but the addition of cellobiose did not, suggesting that their appearance is not due to a cellobiose-oxidizing enzyme. No accumulation of oxidized cello-oligosaccharides occurred when the action of both cellobiohydrolases (CBH I and II) was simultaneously blocked by monoclonal antibodies. These data suggest that cellulose already contains oxidized chain termini, and that these aldonolactones and aldonic acids are released by the action of the two cellobiohydrolases and not by a ‘cellulose-oxidizing’ enzyme.


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