Cyclomaltodextrins

Essentials of Carbohydrate Chemistry Springer-Verlag New York Inc. 1998 

The cyclomaltodextrins have a curious water solubility in which the molecules with an even number of D-glucose residues are much more water soluble than are the molecules with an odd number of D-glucose residues [7,14]. The properties and characteristics of the cyclomaltodextrins are sunmiarized in Table 8.1. 

One of the most impressive properties of the cyclomaltodextrins is their ability to form inclusion complexes with a wide variety of organic and inorganic compounds. Many of these complexes form crystals, and they have been the basis for the development of separation and purification schemes for the 

Benzene Fluorobenzene Chlorobenzene Bromobenzene /7-Cymene Cyclohexanol 1,1,2,2-Tetrachloroethane Tetrachloroethylene Anthracene 

The internal hydrophobic cavity is the key structural feature of the cyclodex-trins it provides their ability to complex and hold a wide variety of inclusion molecules. Differences between the cyclomaltodextrins arise from differences in the diameters of their cavities. The organic inclusion molecules have alkyl, aromatic, alcohol, and ester groups. To bind with the cyclomaltodextrin, the inclusion molecule must have a size that fits, at least partially, into the cavity, creating the complex. The inclusion compound, however, does not have to be completely contained in the cavity. Complexes can be formed by the insertion of some specific functional group or part of the molecule to bind in the hydrophobic cavity. This partial insertion of the inclusion compound gives a cap or lid on the cavity. Sometimes more than one cyclodextrin will bind with a single inclusion molecule. 

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An export-affinity fusion vector containing the gene cgt encoding cyclomaltodextrin glucanotransferase (CGTase) from Bacillus circulans var. alkalophilus has been described... 

Primary, secondary and tertiary structures of amylolytic enzymes from a wide variety of sources and functions (the a-amylases, bacterial cyclomaltodextrin glucanosyltrans-ferases, isoamylases and starch-branching enzymes) have been found to be closely related, and have been placed into the so-called structural a-amylase family.176,177 These enzymes have been studied with regard to the number, structure, organization and function of domains.178... 

A. oryzae a-amylase consists of three domains (A, B and C).179,180 Domain A has an amino-terminal ((3/a)8-barrel structure, followed by domain C, consisting of (3-strands that are folded into a Greek motif. Domain B is inserted between the third (3-strand and the third a-helix of the ((3/a)8-barrel. This is a highly variable domain in both its length and amino acid sequence, depending on the source and type of the enzyme.181,182 Cyclomaltodextrin glucanosyltransferases generally consist of five domains (A, B, C, D and E). Domains A, B and C consist of the same catalytic domains found in... 

A few chimeric enzymes have been constructed by adding one or more domains from one amylolytic enzyme to another. Some of these chimeric enzymes have been studied in regard to the secretion of the enzyme,187 substrate specificity188 and product specificity.189 A starch binding domain from a Bacillus sp. cyclomaltodextrin glucanosyltransferase was fused with B. subtilis a-amylase, and an a-amylase was... 

An identical mechanism can be postulated for hydrolysis of the a-(l—>6) branch linkage by isoamylases and for cyclomaltodextrin glucanosyltransferase. For the latter enzyme, the water molecule is replaced by the C-4 hydroxyl group on the nonreducing end glucosyl unit of the starch chain (Figure 7.6). 

Figure 7.17 Structures of active-site directed amylase inhibitors. The K values are for glucoamylase (GA), porcine pancreatic oamylase (PPA) and cyclomaltodextrin glucanosyltransferase (CGTase).

Villette, J.R., Helbecque, N., Albani, J.R., Sicard, P.J. and Bouquelet, S.J. (1993). Cyclomaltodextrin glucanotransferase from Bacillus circulans E 192 nitration with tetranitromethane. Biotechnology and Applied Biochemistry, 17, 205-216. 

The cyciomaitodextrins (a-CD, -CD, and y-CD) can be selectively obtained from a fermentation culture or an enzyme digest of cyclomaltodextrin glucanotransferase reaction with solubilized starch. The majority of the cyclomaltohexaose (a-CD) can be separated from cycloma-Itoheptaose (/3-CD) and y-CD by their selective precipitation with p-cymene from the culture supernatant or from an enzyme digest [168]. The a-CD can then be precipitated from the supernatant with cyclohexene, which is extracted with acetone to remove the cyclohexene and the a-CD can be crystallized from water or a propanol-1/water solution [169]. The p-cymene precipitates of /3-CD and y-CD are put into a water solution and /3-CD selectively precipitated from y-CD with fluorobenzene. The y-CD is then precipitated with anthracene saturated in diethyl ether. After the removal of the fluorobenzene from /3-CD with acetone or ethanol extraction, /3-CD can be crystallized from water, and after the removal of anthracene with acetone or ethanol extraction from y-CD, it can also be crystallized from water [170,171]. The selective precipitations of the cyciomaitodextrins with various organic molecules is based on the selective formation of complexes of the organic molecules with the specific sizes of the cyciomaitodextrins and the relatively hydrophobic interior cavities of the cyciomaitodextrins [166,167,168]. 

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