Synthesis of highly ordered cellulose II in vitro using cellodextrin phosphorylase

Synthesis of cellulose in vitro is expected to afford tailor-made cellulosic materials with highly homogeneous structure compared to natural cellulosic materials. Here we report the enzymatic synthesis of cellulose II with high crystallinity from glucose and α-glucose 1-phosphate (αG1P) by cellodextrin phosphorylase (CDP). Although glucose had been believed not to act as a glucosyl acceptor of CDP, a significant amount of insoluble cellulose was precipitated without accumulation of soluble cello oligosaccharides when glucose was mixed with αG1P and CDP. This phenomenon can be explained in terms of the large difference in acceptor reactivity between glucose and cello oligosaccharides. 1H NMR spectrometric analysis revealed that this insoluble cellulose had an average degree of polymerization (DP) of nine. TEM observation, together with electron and X-ray diffraction studies, indicated that the insoluble cellulose formed platelet-shaped single lamellar crystals of cellulose II, several μm in length and several hundred nm in width; this is large compared to reported cellulose crystals. The thickness of the lamellar crystal is 4.5 nm, which is equivalent to a chain length of a cello oligosaccharide with DP nine and is consistent with the 1H NMR spectroscopic results. These results suggest that cello oligosaccharides having an average DP of nine are synthesized in vitro by CDP when glucose is used as an acceptor, and the product forms highly crystalline cellulose II when it precipitates.

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