Starch bound enzyme

Diabetic patients have reduced antioxidant defences and suffer from an increased risk of free radical-mediated diseases such as coronary heart disease. EC has a pronounced insulin-like effect on erythrocyte membrane-bound acetylcholinesterase in type II diabetic patients (Rizvi and Zaid, 2001). Tea polyphenols were shown to possess anti-diabetic activity and to be effective both in the prevention and treatment of diabetes (Choi et al, 1998 Yang et al, 1999). The main mechanism by which tea polyphenols appear to lower serum glucose levels is via the inhibition of the activity of the starch digesting enzyme, amylase. Tea inhibits both salivary and intestinal amylase, so that starch is broken down more slowly and the rise in serum glucose is thus reduced. In addition, tea may affect the intestinal absorption of glucose. 

Proteins, particularly granule-bound starch synthesis enzymes entrapped in dried starch granules, are also involved in the determination of the starch-pasting characteristics, even when they are present at less than 0.2% in dried starch. Figure... 

UDP-Glc essentially vanished. Either the activity observed with UDP-Glc was not solubilized, suggesting that a different enzyme catalyzed the UDP-Glc activity, or became inactive during the amylase procedure. Alternatively, the ability of the starch-bound starch synthase to utilize UDP-Glc is dependent on the close association of the enzyme with the starch granule. In other words, the conformation of the GBSS is altered in the presence of starch to allow UDP-Glc to be catalytically active. 

A C. reinhardtii mutant lacking D-enzyme activity has been characterized and has been shown to have significantly lower levels of starch. Other enzymes involved in starch metabolism such as ADP-Glc PPase, granule-bound and soluble starch synthase, BE, phosphorylase, a-glucosidase, amylases, and debranching enzyme activities were not affected. The starch content in the mutant was about 6-13% of wild type and there was an excessive accumulation of maltooligosaccharides up to a polymer size of 16 glucose units. 

Haltohexaose-producing Amylases. Both endo- and exo-amylases that produce maltohexaose from starch have been identified and characterized. The exo-acting enzyme was first discovered as a cell bound enzyme in "Aerobacter aerogenes (now called Klebsiella pneumoniae), an organism better known for pullulanase synthesis. The enzyme is stable at temperatures lower than 50< C and has an optimum pH for activity around neutrality (39). Escherichia coli, long thought to be devoid of amylase activity, has been shown to synthesize a similar enzyme (40). These enzymes are periplasmic and synthesis is induced by the presence of maltose (40). 

Glucose molecules are bound in starch by the easily hydrolyzed a bonds. The same type of bond can also be seen in the animal reserve polysaccharide glycogen. This is in contrast to many structural polysaccharides such as chitin, cellulose and peptidoglycan, which are bound by P-bonds and are much more resistant to hydrolysis. A starch branching enzyme introduces 1,6-a glycosidic bonds between these chains, creating the branched amylopectin (Figure 5.28). 

Table III compares the biochemical features of the B-amylase which was purified to homogeneity from C. thermosulfurogenes (74). The enzyme is a tetrameric glycoprotein with an apparent molecular weight of 210,000. The thermophilic B-amylase binds tightly to raw starch presumably by glycoconjugate forces and it is still active while bound to starch (75). This feature has been used for improved affinity purification of the enzyme using raw starch (76).

Binding enzymes to solid supports can be achieved via covalent bonds, ionic interactions, or physical adsorption, although the last two options are prone to leaching. Enzymes are easily bound to several types of synthetic polymers, such as acrylic resins, as well as biopolymers, e.g., starch, cellulose [52], or chitosan [53,54]. Degussa s Eupergit resins, for example, are used as enzyme carriers in the production of semisynthetic antibiotics and chiral pharmaceuticals [55], Typically, these copolymers contain an acrylamide/methacrylate backbone, with epoxide side groups... 

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