Cyclomaltodextrin

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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