[Degradation of Maillard reaction products by amylolytic enzymes. 3. Inhibition of glucoamylase, alpha-amylase and alpha-glucosidase by heat treated alpha-glucans and melanoidins]

Amylolytic enzymes are only slightly inhibited by thermal treated alpha-glucans (10-15%). The addition of glycine to the thermolysis mixture produces no increase of the inhibition. The inhibition of the enzyme activity is probably caused by short-chain alpha-glucans that the secondary binding places of the active centre coat and therefore the hydrolysis is reduced. Glucoamylase and alpha-amylase are not inhibited by non-dialysed melanoidines from the reaction of D-glucose and glycine, but there is a strong inhibition of alpha-glucosidase by these melanoidines (up to 45%). Strongly coloured, low molecular compounds that are formed during the Maillard-reaction and are soluble in ethyl acetate cause no inhibition of Glucoamylase and alpha-amylase.

Amylolytic enzymes and products derived from starch: a review

This review provides current information on starch and its molecular composition, common and potential sources, and manufacturing processes. It also deals with the five groups of enzymes involved in the hydrolysis of starch: the endo- and exoamylases, which act primarily on the alpha-1,4 linkages; the debranching enzymes, which act on the alpha-1,6 linkages; the isomerases which convert glucose to fructose; and the cyclodextrin glycosyltransferases which degrade starch by catalyzing cyclization and disproportionation reactions. This work mainly discusses the enzymatic processes for the manufacture of maltodextrins and corn syrup solids, including the production, both batch and continuous, of glucose syrup, and the processes to obtain sweeteners, such as maltose and 42, 55, and 90% high-fructose corn syrups. It highlights the novel production of Schardinger's dextrins: the alpha-, beta-, and gamma-cyclodextrins, consisting of six, seven, and eight glucose monomers, respectively. New products are emerging on the market that can serve as fat and oil substitutes, moisture-retention compounds, crystal-formation controllers, stabilizers for volatile materials like flavors and spices, or products for the pharmaceutical industry. As a result, particular attention is given to functional properties and applications of the above-cited compounds.

Detection of a covalent intermediate in the mechanism of action of porcine pancreatic alpha-amylase by using 13C nuclear magnetic resonance

The catalytic mechanism of porcine pancreatic alpha-amylase (1,4-alpha-D-glucan glucanohydrolase, EC 3.2.1.1) has been examined by nuclear magnetic resonance (NMR) at subzero temperatures by using [1-13C]maltotetraose as substrate. Spectral summation and difference techniques revealed a broad resonance peak, whose chemical shift, relative signal intensity and time-course appearance corresponded to a beta-carboxyl-acetal ester covalent enzyme-glycosyl intermediate. This evidence supports a double-displacement covalent mechanism for porcine pancreatic alpha-amylase-catalyzed hydrolysis of glycosidic linkages, based on the presence of catalytic aspartic acid residues within the active site of this enzyme.

Selective inhibition of histidine-modified pancreatic alpha-amylase by proteinaceous inhibitor from Phaseolus vulgaris

Chemical modification of two histidine residues of porcine pancreatic alpha-amylase (EC 3.2.1.1) by diethyl pyrocarbonate in the presence of a high concentration of maltotriose caused a decrease of amylase activity and an increase of maltosidase activity (hydrolysis of p-nitrophenyl-alpha-maltoside). By binding a proteinaceous inhibitor from Phaseolus vulgaris (white kidney bean) with the modified enzyme, the amylase activity was further decreased but the maltosidase activity was retained to about 100% that of the native enzyme. Both amylase and maltosidase activities of the native enzyme were almost completely inhibited by the proteinaceous inhibitor. The increase of maltosidase activity by histidine modification was due to an increase of kcat, whereas the Km value was not changed; but binding of the proteinous inhibitor affected mainly the Km value of the modified enzyme.

Activity and action pattern of Bacillus licheniformis alpha-amylase in aqueous ethanol

A purified B. licheniformis alpha-amylase in a mixture of ethanol-aqueous buffer (1:1, v/v) retains half the activity shown in water alone. In ethanol-aqueous buffer (7:3, v/v) about 20% of the activity is retained. The pattern of oligosaccharides produced from amylose changed with ethanol concentration; in aqueous buffer the products are: DP 1 and 2, 33.7%; DP 3, 28.5%; DP 4, 4.4% and DP 5, 33.4%. Whereas in ethanol-aqueous buffer (7:3, v/v) the products are DP 1 and 2, 66.8%; DP 3, 17.3%; DP 4, 4.1% and DP 5, 11.8%. These results suggest that a change in substrate affinity at the active centre subsites is induced in the ethanol-aqueous buffer medium.