β-Chitin microfibrils were treated with ChiA and ChiB (chitinases A and B respectively) from Serratia marcescens 2170. The β-chitin microfibrils were shortened, and the tips appeared narrowed and sharpened at both ends, after either consecutive or simultaneous degradation by ChiA and ChiB. Increased production of reducing sugars by simultaneous degradation (by ChiA and ChiB) of β-chitin, but not of glycol chitin, suggests synergistic interactions between the two enzymes. A combined analysis using the tilt microdiffraction method to determine the crystallographic axes, together with the biotin–streptavidin–gold-labelling method specific to the reducing ends, was used to investigate the polarity of the degraded β-chitin microcrystals. The digestion of the β-chitin fibrils by ChiA occurred from the reducing end to the nonreducing end, whereas digestion by ChiB occurred from the non-reducing end to the reducing end. The results are in agreement with the previously determined three-dimensional structures of these enzymes.

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