Starch enzymic synthesis

Manners, D. J., Enzymic Synthesis and Degradation of Starch and Glycogen, 17, 371-430... 

Although TA from yeast is commercially available, it has rarely been used in organic synthesis applications, and no detailed study of substrate specificity has yet been performed. This is presumably due to high enzyme cost and also since the reaction equilibrium is near unity, resulting in the formation of a 50 50 mixture of products. In addition the stereochemistry accessible by TA catalysis matches that of FruA DHAP-dependent aldolase and the latter is a more convenient system to work with. In one application, TA was used in the synthesis D-fructose from starch.113 The aldol moiety was transferred from Fru 6-P to D-glyceraldehyde in the final step of this multi-enzyme synthesis of D-fructose (Scheme 5.60). This process was developed because the authors could not identify a phosphatase that was specific for fructose 6-phosphate and TA offered an elegant method to bypass the need for phosphatase treatment. 

One of the main characteristics of this enzyme system is the unique role played by sucrose as the donor of D-glucosyl groups. Even the closely allied isomer, a-D-galactopyranosyl /3-n-fructofuranoside is inactive in this enzymic reaction. The results of work on the enzymic synthesis of starch from D-glucosyl phosphate raised a question as to whether a phosphoryla-... 

It appears that phosphorus is related to the formation of starch in the plant. Thus Hanes has synthesized a linear polysaccharide from a-D-glucopyranosc 1-phosphate (Cori ester) through the action of potato phosphorylase. Dunlap and Beckmann and likewise Cori have found that the B-fraction activates this enzymic synthesis, while the A-frac-tion is inactive. It has not been established whether this effect is due to the branched character of the B-fraction or to the presence of phosphate in its structure. 

The continuing interest of Bourne in the chemistry of polysaccharides and associated enzymes originated from the work of Haworth and Peat directed towards the enzymic synthesis and degradation of starch. The impetus for this work was given by the discovery, made by C. S. Hanes in 1940, that a phosphorylase isolated from the potato and pea effects the synthesis, from D-glucosyl phosphate, of starch, later shown (by Haworth, Heath, and Peat) to be amylose. In his first paper (with Haworth and Peat) in 1944, Bourne described the isolation of the Q-enzyme which, in conjunction with phosphorylase, effects the conversion of D-glucosyl phosphate into the major component of whole starch, namely, amylopectin. He had discovered the Q-enzyme in a fraction discarded by previous workers. Already, the quintessence of his mind was revealed in this work meticulous attention to detail, and perception of essentials. 

The Enzymic Synthesis and Degradation of Starch. Part VIII, The Use of Mixtures of P- and Q-Enzymes in the Synthesis of Starch-type Polysaccharides, S. A. Barker,... 

With the recent identification of the anomalous linkages in amylose as a-D-(l 6)-glucosidic inter-chain linkages, the metabolism of starch and glycogen can be adequately considered in terms of the enzymic synthesis and degradation of only two types of n-glucosidic linkage, namely, a-D-(l— 4) and a-n-(l- ). 

Figure 14.2-4. Multi-enzyme synthesis of D-Fru from starch.

TA is also an enzyme of the oxidative pentose phosphate pathway[218). It catalyzes the transfer of the C1-C3 aldol unit from D-sedoheptulose 7-phosphate to D-Gly 3-P, and produces D-Fru 6-P and D-erythrose 4-phosphate (Fig. 14.2-3). TA forms a Schiffbase intermediate and does not require any co-factors. This enzyme is commercially available, and was used in a multi-enzyme synthesis of D-Fru from starch (Fig. 14.2-4) 1233] Here, it accomplished transfer of an aldol moiety from Fru 6-P to d-glyceraldehyde, and formed D-Gly 3-P and D-Fru. 

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