W. Banks

The interaction of linear, amylose oligomers with iodine

A series of linear, amylose oligomers has been synthesized enzymically to yield samples having the number-average degree of polymerisation, DPn¯, in the range 22 to 134. The interaction of these materials with iodine has been studied. The wavelength of maximal absorption of the iodine complex, λmax, has been found to be related to DPn¯ by the Langmuir isotherm: 1/λmax⁡=1.558×10−3+102.5×10−4(1/DPn¯). Differential, potentiometric titration of iodine has shown that the iodine-binding capacity of the linear oligomers is a function of both DPn¯ and temperatures. The enthalpy of the iodine uptake has been measured, and found to be a function of DPn¯ for values of DPn¯<200.

Studies on starch degrading enzymes

Abstract The action pattern on amylose of the alpha-amylases from B. subtilis, human saliva, malted rye, and porcine pancreas has been studied. In the initial stages, the reaction has been followed by measuring the weight-average degree-of-polymerization ( DP w ) by viscometry, and also the number-average value ( DP n ) by enzymic assay. The mode of enzymic hydrolysis was established by following changes in the value of the ratio DP w / DP n , and also by chromatographic examination of the products of low molecular weight. We have confirmed that the porcine, pancreatic alpha-amylase is unique amongst those enzymes examined, in showing evidence of multiple attack at certain pH-values, and have shown that the presence of glycerol (40%, v/v) changes the mode of action in the initial stages to an essentially random form. The significance of this finding is discussed.

The conformation of amylose in neutral, aqueous salt solution☆

Abstract Linear amylose has been subfractionated, and the hydrodynamic properties of the fractions examined. From measurements of the limiting-viscosity number, [ n ], in 0.33m potassium chloride, and of the weight-average molecular weight, M w , by light scattering on the acetate, the relation was found. The significance of the exponent in this relation and others in the literature is discussed. Estimations of the “stiffness” of the amylose molecule in aqueous solution have been obtained for various model systems, i.e., the Kuhn statistical length, the Kratky-Porod persistence length, and Nagais theory for a mixture of helical and randomly coiled segments. The results of each individual theory are ambiguous. It is shown, on the basis of Nagais theory, that there is definite evidence for the absence of rigid helical segments in amylose in aqueous solution. The temperature coefficient of [ n ] for amylose in aqueous solution is also discussed.

The hydrodynamic behaviour of native amylose in good solvents

Abstract Viscosity measurements on 12 fractions of linear amylose have been made in three thermodynamically good solvents—formamide (F), methyl sulphoxide (Me2SO), and aqueous potassium hydroxide (KOH). The following Mark-Houwink relations were obtained: [ η ] F = 3.05 × 10 − 2 M ¯ ω 0.62 , [ η ] M e 2 S O = 1.51 × 10 − 2 M ¯ ω 0.70 , and [ η ] K O H = 8.36 × 10 − 3 M ¯ ω 0.77 . The Kamide-Inamoto and Stockmayer-Fixman-Burchard theories show that the amylose molecules in these solvents are extended as a result of solute-solvent interaction and there is little evidence of any free-draining characteristics. The graph of [η]/M1/2 againstM1/2 for all three good solvents is linear with a common intercept. Incidently, this intercept is the same as that for an aqueous theta-solvent, showing that the basic skeletal structure of amylose is the same in each of these solvents. The conformation of amylose in these three good solvents is regarded as being that of a random coil with negligible helical character.

The conformation of amylose in alkaline salt solution

Abstract The conformation of amylose in various solvents is discussed. It is shown that the changes in molecular volume of the polysaccharide (measured by viscosity) as potassium chloride is added to a solution of amylose at pH 12 are similar to those obtained on adding butan-1-ol to the solution. The viscosity number in both cases decreases to values less than that observed for amylose in water, in which Flory theta-conditions are approximated. The minimum value of the viscosity number, in fact, is identical to that observed on the addition of butan-1-ol and iodine to neutral aqueous solution of amylose—conditions known to result in a helical complex. It is concluded that amylose undergoes a coil-to-helix transition as potassium chloride is dadde to solutions of the polysaccharide at pH 12.

A novel method of determining the number-average degree of polymerization of linear maltodextrins and amylose

Abstract An enzymic method for determining the number-average degree of polymerization ( D P ¯ n ) of maltodextrins and amylose is described. In this technique, the D -glucans are treated with β-amylase under conditions in which enzymic degradation is complete, i.e., molecules having an even number of residues form maltose, and molecules having an odd number of residues yield maltose and one D -glucose unit. The amount of D -glucose is estimated by using glucose oxidase. The total concentration of the D -glucan itself is measured by use of amyloglucosidase. Hence, on the basis that the sample contains equal numbers of molecules having odd and even numbers of D -glucose residues, D P ¯ n can be calculated. Experimental conditions for this assay are discussed, and the accuracy of the technique has been confirmed by using (a) pure maltodextrins, and (b) synthetic mixtures of two degraded amyloses of D P ¯ n ca. 400 and 8. The method has been found to be applicable to linear amylose; D P ¯ n values greater than 1000 can be obtained to within 5%.

Light-scattering studies on aqueous solutions of amylose and amylopectin

Abstract Light-scattering studies have been made on amylose and amylopectin in water. True scattering intensities of the solvent were obtained by degrading the polysaccharide solutions with alpha-amylase in the light-scattering cell. This technique enables the molecular parameters of size and shape to be obtained more speedily and accurately than hitherto. In addition, information regarding the contribution of dust to the scattering intensity of a polymer solution was obtained.

Physico-chemical studies on starches: Part XXXIV. The distribution of molecular weight in amylose samples obtained by the leaching and the dispersion of potato starch

Abstract Leached and total amylase from potato starch have been subfractioned by fractional precipitation. The former has been shown to have an exponential distribution of molecular weights as expected for a random A - A type polymer. The distribution of molecular weight for the total amylose is much broader, compatible with the presence of a branched fraction.

Studies on starch-degrading enzymes : Part XIV. The multiple forms of porcine, pancreatic alpha-amylase

Abstract Crystalline, porcine, pancreatic alpha-amylase has been fractionated into four distinct fractions by ion-exchange chromatography on DEAE-cellulose. Each fraction hydrolyses amylose in a manner identical to that of the parent enzyme, i.e., at optimal pH, the reaction pattern corresponds to multiple attack, whereas in the presence of glycerol, or at high pH, it changes to multichain attack. Ultracentrifugation and gel exclusion-chromatography showed that the molecular weights of the fractions are similar to one another and to the parent enzyme, suggesting that the fractions are isoenzymes. However, determination of the amino-acid content of the multiple forms failed to reveal any reason for their different migratory rates through DEAE-cellulose. It is suggested that the multiple forms are artefacts, arising during the isolation of the enzyme.