Glucans, cyclic

Fig. 6.—One of the Molecular-ion Clusters Obtained from a Sample of Deuteropermethy-lated. Cyclic /3(l- 2)-Glucans (see Section VI,S). [All high-mass samples give unresolved clusters of this type if the mass spectrometer is operated at low resolution. The peak is 6 mass units wide at half height. The mass is assigned by using the mass marker, which gives marks every 4 mass units, as shown. The center of the peak corresponds to the chemical molecular weight of an [M + NKJ species.]...

Cyclodextrins (CDs) were first observed by Villiers (i) nearly a century ago. First thought to be a mysterious crystalline form of starch, the structure and chemistry of these unique cyclic glucan oligosaccharides have been elucidated through the contributions of Schardinger, Freudenburg, Cramer and French (2). 

The resulting increased turgor in the periplasm is thought to buffer the cytoplasm against the loss of external osmolarity and to protect the periplasmic space from being eliminated by expansion of the plasma membrane. Related cyclic glucans, which are attached to sn-1 -phosphoglycerol or O-succinyl ester residues, are accumulated by rhizobia.s... 

A. Dell, W. S. York, M. McNeil, A. G. Darvill, and P. Albersheim, Host-symbiont interactions 14. The cyclic structure of beta-D-(l,2)-linked D-glucans secreted by rhizobia and agrobacteria, Carbohydr. Res., 117 (1983) 185-200. 

I. Komanieacka and A. Choma, Isolation and characterization of periplasmic cyclic p-glucans of Azorhizobium caulinodans, FEMS Microbiol. Lett., 227 (2003) 263-269. 

Takaha, T., Yanase, M., Takata, H., Okada, S., and Smith, S. M. 1996. Potato D-enzyme catalyzes the cyclization of amylase to produce cycloamylose, a novel cyclic glucan. J. Biol. Chem.,271, 2902-2908. 

Takata, H., Takaha, T., Okada, S., Hizukuri, S., Takagi, M., and Imanaka, T. 1996. Structure of the cyclic glucan produced from amylopectin by Bacillus starother-mophilus branching enzyme. Carb. Res., 295, 91-101. 

The enzyme activity is widely distributed in bacteria, yeasts, plants, and animals, and catalyzed by at least live structurally distinct enzyme groups (Takaha and Smith, 1999) as shown in Table 28.3. In addition to the inter-molecular trans-glycosylation reaction expressed in equation (4), 4aGT also catalyze the intramolecular transglycosylation reaction (cyclization reaction) of a-1,4 glucan to produce cyclic a-1,4 glucan as shown in equation 28.5 ... 

We have tested various 4aGTs for their ability to produce cyclic a-1,4 glucan from amylose, and now have the view believe that a cyclization reaction is the common feature of this enzyme (Fujii et al., 2003 Yanase et al., 2002). However, the smallest cyclic glucan produced is greatly dependent on the type of enzyme employed (Table 28.2). In addition to two transferase activities described above, some 4aGTs also exhibit week hydrolitic activity (Fujii et al., 2005a). 

Enzyme Group CAZy family a) Smallest donor b) Smallest acceptor b) Smallest transferred unitb) Smallest cyclic glucan (DP) ... 

As described, cyclic a-1,4 glucan can be produced by the cyclization reaction of 4aGTs on amylose. The smallest cyclic glucan produced is dependent on the type of enzyme employed (Table 28.3). Yield of cyclic glucan appeared to... 

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