Phosphated starches reactions

The reaction catalyzed by phosphorylase. An oxygen of a phosphate ion attacks C-1 of the terminal glucosyl unit of starch or glycogen, displacing the macromolecule and generating glucose-1-phosphate. The reaction proceeds with retention of configuration, a fact... 

Starches have been chemically modified to improve their solution and gelling characteristics for food applications. Common modifications involve the cross linking of the starch chains, formation of esters and ethers, and partial depolymerization. Chemical modifications that have been approved in the United States for food use, involve esterification with acetic anhydride, succinic anhydride, mixed acid anhydrides of acetic and adipic acids, and 1-octenylsuccinic anhydride to give low degrees of substitution (d.s.), such as 0.09 [31]. Phosphate starch esters have been prepared by reaction with phosphorus oxychloride, sodium trimetaphosphate, and sodium tripolyphosphate the maximum phosphate d.s. permitted in the US is 0.002. Starch ethers, approved for food use, have been prepared by reaction with propylene oxide to give hydroxypropyl derivatives [31]. 

Granular starch has been cross-linked with phosphate by reaction of an aqueous alkaline suspension at pH 8-12 with 0.005-0.25% phosphorus oxychloride [15] (reaction 7.15). If starch granules are treated with 1% or higher concentrations of phosphorus oxychloride, the granules become very resistant to gela-tinization. Trimetaphosphate has also been used to produce phosphate cross-linkages [15] (reaction 7.16). Phosphorylation of 0-6 is predominant, and that of 0-3 is minimal [19]. 

FIGURE 7.23 The starch phosphorylase reaction cleaves glucose residues from amy-lose, producing a-D-glucose-l-phosphate. 

Starch molecules have many exposed O—bonds, so this phosphorylation reaction results in multiple phosphate groups attached to each starch molecule. The remaining —OH group on each phosphate can condense with an O— H bond on another starch molecule. This cross-linking of starch chains gives the desired thick consistency of puddings and pies. 

The construction of the structural kinetic model proceeds as described in Section VIII.E. Note that in contrast to previous work [84], no simplifying assumptions were used the model is a full implementation of the model described in Refs. [113, 331]. The model consists of m = 18 metabolites and r = 20 reactions. The rank of the stoichiometric matrix is rank (N) = 16, owing to the conservation of ATP and total inorganic phosphate. The steady-state flux distribution is fully characterized by four parameters, chosen to be triosephosphate export reactions and starch synthesis. Following the models of Petterson and Ryde-Petterson [113] and Poolman et al. [124, 125, 331], 11 of the 20 reactions were modeled as rapid equilibrium reactions assuming bilinear mass-action kinetics (see Table VIII) and saturation parameters O1 1. 

This enzyme [EC 2.4.1.1], also called phosphorylase, catalyzes the reaction of [(l,4)-o -D-glucosyl] with orthophosphate to produce [(l,4)-o -D-glucosyl] -i and a-D-glucose 1-phosphate. The name to be used with this enzyme is dependent on the naturally occurring substrate for example, glycogen phosphorylase, starch phosphorylase, maltodextrin phosphorylase, etc. 

The function of the sulfate residue in these polysaccharides is unknown but the suggestion has been made that just as starch is synthesised from D-glucose 1-phosphate by the action of phosphorylase, so the seaweed polysaccharides are formed from the appropriate sugar sulfate by reaction with a sulfatase. ... 

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