Amylose cycloamyloses from

Amylose gives a greater yield of cycloamyloses than amylopectin. Kerr obtained 70% of cycloamyloses from corn amylose and from amylopectin 44%. Cycloamyloses are formed also from glycogen. On the other hand the /8-dextrin yields no cycloamyloses. " The conclusion is inescapable that the cycloamyloses are formed from the simple chains of the amylose and from the end chains of amylopectin and glycogen. 

The c.d. spectra of amylose and cycloamylose have been measured at different temperatures in vacuum u.v. The spectral contributions of interior groups of amylose differ from those of cycloamylose. Very similar c.d. spectra were obtained for samples of aqueous amylose and amylose-butan-l-ol complexes, which suggests that the conformational change of the maltosyl subunits of amylose upon complexation is small. This is consistent with a model for amylose in which the occupied conformational space is a small region which includes the V-form helix point, and with the idea that amylose in aqueous solution is a loose, extended... 

Values of /c2 and Kd for the reactions of the cycloamyloses with a variety of phenyl acetates are presented in Table IV. The rate constants are normalized in the fourth column of this table to show the maximum accelerations imposed by the cycloamyloses. These accelerations vary from 10% for p-f-butylphenyl acetate to 260-fold for m-f-butylphenyl acetate, again showing the clear specificity of the cycloamyloses for meta-substituted esters. Moreover, these data reveal that the rate accelerations and consequent specificity are unrelated to the strength of binding. For example, although p-nitrophenyl acetate forms a more stable complex with cyclohexa-amylose than does m-nitrophenyl acetate, the maximal rate acceleration, h/kan, is much greater for the meta isomer. 

Figure 23.9 Adapted from crystallographic coordinates deposited with the Protein Data Bank. PDB ID 4TF4. Sakon, J., Irwin, D. Wilson, D.B., Karplus, P.., Structure and Mechanism of Endo/ Exocellulase E4 from Thermomonospora Fusca. Figure 23.10 is adapted from crystallographic coordinates deposited with The Protein Data Bank, PDB ID 1C58, Gessler, K., Uson, I., Takahan, T., Krauss, N., Smith, S.M., Okada, G.M., Sheldrick, G.M. Saenger, W., V-Amylose at Atomic Resolution X-ray Structure of a Cycloamylose with 26 Glucose Residues (Cycloamaltohexaicosaose). Proc. Nat. Acad. Sci. USA, 1999, 96, 4246.

Studies of the hydrolyses of cyclohexa-, cyclohepta-, and cyclo-octa-amyloses by Taka-amylase A (one of the a-amylases from Aspergillus oryzae) indicated that each cycloamylose binds to the same active site of the enzyme. Since there is little difference in the respective AG, Af/, and AS values for enzymic hydrolysis of these cycloamyloses, their binding modes appear to be similar. The extent of multiple attack on the cycloamyloses was not affected by temperature. A 4-phenylazobenzoyl derivative of Taka-amylase A has been used to investigate the active site of the enzyme. A. oryzae a-amylase has a synergistic effect on the action of the glucoamylase from A. awamori var. kawachi ... 

Hydrated cycloocta-amylose crystallizes as a monoclinic P2j space group with dimensions a = 20.25, b = 10.49, and c = 16.89 A with the angle being 105.32°. The macrocyte has an open structure but displays significant deviations from ideal 8-fold molecular symmetry. Of the 19 water molecules so far identified, 12 may be characterized as being in the torus of the cycloamylose. 

Cyclodextrin n-Glucanotransferase.—Cyclodextrin D-glucanotransferase has been prepared from culture fluids of a Bacillus species by adsorption onto corn starch, fractional precipitation with ammonium sulphate, ion-exchange chromatography, and gel filtration. Disc electrophoresis and isoelectric focusing separated the enzyme into two fractions (p7 6.07 and 6.80), which were able to synthesize cycloamyloses (predominantly cyclohepta-amylose) from starch. The enzymes differ from the cyclodextrin o-glucanotransferase from B. macerans, notably in their actions on starch. 

In the biological synthesis of ( clohexa-, cyclohepta-, and cyclo-octa-amyloses by the action of enzymes from Bacillus megaterium and B. macerans on P C]-starch, the amounts of each cycloamylose formed were determined by measurement of the radioactivity. The cycloamyloses were produced by the respective enzymes in the ratios 1 2.4 1 and 2.7 1 1 and the ratios were largely independent of the pH of the media. Cyclohexa- and cyclo-octa-amyloses were produced directly from starch and not by way of cyclohepta-amylose. 

The stereospecificity of the interactions of several spin-labelled substrates with cyclohexa- and cyclohepta-amyloses, as models for chymotrypsin, has been studied. Complexes of the cycloamyloses with 2,2,6,6-tetramethyl-4-oxy-pyridyl-1-oxide in aqueous solution were examined by e.s.r. spectroscopy the nitroxide function moved to a relatively hydrophobic environment on binding to cyclohepta-amylose, and lost some freedom of rotation on binding to both cycloamyloses. The dissociation constant for the cyclohexa-amylose complex of the nitroxide is greater than that for the cyclohepta-amylose complex, consistent with measurements made on molecular models. In the hydrolysis of the asymmetric compound 3-carboxy-2,2,5,5-tetramethylpyrrolidyl-l-oxide 3-nitro-phenyl ester, catalysed by cyclohexa-amylose, enantiomeric specificity was observed in the acylation step but not in formation of the Michaelis complex , or on hydrolysis of the acylated cycloamylose intermediate. No differences were found in the e.s.r. spectra of solutions of the trapped acylcyclohexa-amylose intermediates derived from ( + )- and ( )-forms of the asymmetric nitroxide. The nitroxide function is less free to rotate in the acylcycloamylose intermediate than in the Michaelis complex and is not included in the cycloamylose cavity. 

Cyclodextrins, also called cycloamyloses, are a family of compounds made up of sugar molecules bound together in a ring. So they are cyclic oligosaccharides (44). jS-Cyclodextrin is a ring from seven members of amylose and also called cyclohepta amylose. 

A /3-amylase isolated from culture filtrates of Bacillus polymyxa released maltose from amylose-like substrates, but it had only limited or no action on amylopectin, periodate-oxidized amylose, and cycloamyloses. ... 

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