Amylose Phosphates

Phosphorylated forms of the single helix (10.26) should be capable of existence. The flexibility of the glycosidic linkage may allow arrangements with the PO4 groups either on the outside or the inside of such a helix, provided that the general H bonding scheme is satisfactory and that steric requirements are met. Heavily phosphorylated helices may have important bio properties. 

Phosphorylation of the OH group on C 6 of the glucose residues would be expected to lead to double helices with an overall diameter somewhat less than that of B-type DNA. Unless the H-bonding scheme has been radically altered, such a phosphorylated form of B-type amylose should have 2x6 PO4 per turn of the helix with a pitch length 21 A, compared to 2 x 10 PO4 per turn and a pitch of 34 A in B-type DNA (Section 10.4). Amylose adopts a random coil configuration in neutral solution, but high concentrations become unstable and the precipitation of insoluble forms may occur. 

FIGURE 10.7 Crystal structure of p-amylose. Viewed down helical axes and chain direction. Broken lines denote some H bonds. 

FIGURE 10.8 Probable chain structures of gelling agarose. 

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Fig. 11 Effect of amylose on the hardness and disintegration of dicalcium phosphate tablets. (From Ref. 62.)...

In the field of polymer science, the most extensively used transferase is phosphorylase (systematic name (1 4)-a-D-glucan phosphate a-D-glucosyltransferase EC 2.4.1.1). Although this enzyme is responsible for the depolymerization of linear a-( 1 4) glycosidic chains in vivo it can also be used to synthesize linear a-( 1 4) glycosidic chains (amylose) in vitro. 

The fact that glycogen phosphorylase can be used to polymerize amylose was first demonstrated by Schaffner and Specht [110] in 1938 using yeast phosphorylase. Shortly after, the same behavior was also observed for other phosphorylases from yeast by Kiessling [111, 112], muscles by Cori et al. [113], pea seeds [114] and potatoes by Hanes [115], and preparations from liver by Ostern and Holmes [116], Cori et al. [117] and Ostern et al. [118]. These results opened up the field of enzymatic polymerizations of amylose using glucose-1-phosphate as monomer, and can be considered the first experiments ever to synthesize biological macromolecules in vitro. 

Recently Kuriki and coworkers succeeded in producing glucose-1-phosphate in situ during the enzymatic polymerization of amylose. By using sucrose phosphorylase or cellobiose phosphorylase, the monomer was produced during the polymerization from inorganic phosphate and sucrose or cellobiose, respectively [119-121]. 

Arsenate similarly replaces phosphate in various phosphorolysis reactions, so that sucrose phosphorylase catalyzes the hydrolysis of sucrose in its presence (23), potato phosphorylase can hydrolyze amylose and amylopectin (24), nucleoside phosphorylase can hydrolyze inosine... 

Amylose, although water soluble, gives an unstable solution which irreversibly precipitates. It is mainly responsible for the deep blue coloration given by starch and iodine. Solutions of amylopectin are relatively stable. The iodine-binding capacity, on the other hand, is very low. A small amount of covalently bound phosphate normally appears with starch but its exact location within the molecule is not known. 

In sub-FC, a detailed study of the influence of mobile phase additives on the chiral resolution of isoxazoline-based Ilb/IIIb receptor antagonists was carried out by Blackwell [145] on Chiralcel OD-H CSPs. The different mobile phase additives used were acetic acid, trifluoroacetic acid, formic acid, water, triethylamine, triethanolamine, n-hexylamine, trimethyl phosphate, and tri-w-butyl phosphate. In general, n-hexylamine and tri-/ -butyl phosphate mobile phase additives resulted in better resolution. The chiral separation of four 1,3-dioxolane derivatives on an amylose-based column has been described [151]. The effects of mobile phase composition, temperature, and pressure have been investigated. The nature of the modifier is the main parameter it has the highest impact on chiral resolution and is more important than the polarity of the mobile phase. Therefore, the organic modifier that gave the best enantiomeric separation was different for each compound. 

Balmer et al. [60] separated the two enantiomers of omeprazole on three different stationary phases with immobilized protein, viz, Chiral-AGP with a-1 acid glycoprotein, Ultron ES-OVM with ovomucoid, and BSA-DSC with BSA cross-linked into 3-aminopropyl silica using N-suc-cinimidyl carbonate. The mobile phase (1 ml/min) was phosphate buffer solution with 3—10% 2-propanol as the organic modifier. The enantiomers of omeprazole were separated on Chiralpak AD, an amylose-based chiral stationary phase, with ethanol-hexane (1 4) as mobile phase (1 ml/min). 

Substances commonly found in starch granules are amylopectin, amylose, molecules intermediate between amylose and amylopectin, lipid (including phospholipids and free fatty acids), phosphate monoester and proteins/enzymes. The contents and the structures of amylopectin and amylose play major roles in the functional properties of starch. However, lipids, phospholipids and phosphate monoester groups have significant effects on starch functional properties, even though they are minor constituents. 

Swinkels29 collected published characterization data for tapioca starch and compared it to that for other starches of commercial significance (Table 12.4). Tapioca starch is differentiated from other starches by its low level of residual materials (fat, protein, ash), lower amylose content than for other amylose-containing starches, and high molecular weights of amylose and amylopectin. The small amount of phosphorus in tapioca starch is partially removable30 and, therefore, not bound as the phosphate ester as in potato starch. It is also common to find protein and lipid values of zero, as reported by Hicks.31 The very low protein and lipid content is an important factor which differentiates tapioca starch from the cereal starches. 

Amaranth starch has very small and very uniform granules, the majority being less than 1 micrometer in diameter. Starch isolated from two Amaranthus species was compared and found to contain approximately 90% amylopectin and 10% amylose.164 Those authors prepared distarch phosphates and found that A. hypochondriacus starch responded more to crosslinking, as evidenced by reduced swelling power at 85°C and an increased gelatinization temperature range than did A. cruentus starch. 

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