Starch enzymatic polymerization

Eurther conversion (saccharification) to dextrose can be done using glucoamylase. Starch consists of polymeric linear a-1,4 linked dextrose units (amylose, 25 % of the starch) and polymeric mixed a-l,4/a-l,6 linked dextrose units (amylopectin, 75 % of the starch). Eor enzymatic degradation besides a-1,4 specific amylases also a-1,6 specific amylases (pullulanases) are required. A portion of the dextrose can be converted into fructose with a glucose isomerase yielding a high fructose com symp (MFCS). 

Both starch and cellulose are prepared in nature by enzymatic, chain growth polymerization reactions of glucose nucleotide monomers [6]. In both cases, the monomer precursor is glucose-1-phosphate, which is enzymatically converted to the nucleotide derivative. The latter, in turn, complexes with an enzyme to form the activated monomer at the active site on the enzyme, which also contains the growing polymer molecule, as schematically illustrated below for the enzymatic polymerization of cellulose ... 

Biocatalysis is a key route to both natural and non-natural polysaccharide structures. Research in this area is particularly rich and generally involves at least one of the following three synthetic approaches 1) isolated enzyme, 2) whole-cell, and 3) some combination of chemical and enzymatic catalysts (i.e. chemoenzymatic methods) (87-90). Two elegant examples that used cell-fi-ee enzymatic catalysts were described by Makino and Kobayashi (25) and van der Vlist and Loos (27). Indeed, for many years, Kobayashi has pioneered the use of glycosidic hydrolases as catalysts for polymerizations to prepare polysaccharides (88,91). In their paper, Makino and Kobayashi (25) made new monomers and synthesized unnatural hybrid polysaccharides with regio- and stereochemical-control. Van der Vlist and Loos (27) made use of tandem reactions catalyzed by two different enzymes in order to prepare branched amylose. One enzyme catalyzed the synthesis of linear structures (amylose) where the second enzyme introduced branches. In this way, artificial starch can be prepared with controlled quantities of branched regions. 

Any systematic study of cell walls requires an a-D-galacturonanase to release pectic and other matrix components. Molecular structural studies have so far progressed that elaborate models showing the various polymeric constituents in juxtaposition have been generated. After enzymatic elimination of starch and protein, hydrolysis of the residual polysaccharide and estimation of the uronic acids and monosaccharides released furnish considerable information on the composition of agricultural samples. Partial depolymerization affords the complex, well-studied rhamnogalacturonans I and II (RG-I and RG-II). 

OmpF was successfully reconstituted into Upid vesicles (186,218), which could be demonstrated using an encapsulated enzyme, -lactamase, which is able to hydrolyze the antibiotic ampicillin. The hydrolysis product, ampicillinoic acid, can reduce iodine to iodide, which can be monitored by iodometry, ie via the decol-orization of a starch/iodine complex in the exterior solution. The enzyme and the membrane channel have been shown to preserve their activity in the presence of hydrophobic methacrylate monomers before and after their cross-linking polymerization. Polymerization of hydrophobic iV-butylmethacrylate and ethylene glycol dimethacrylate (186) lead to partial expulsion of some reconstituted channels during the cross-linking reaction, thereby decreasing the enzymatic activity. 

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