A-amylase, pancreatic

Pancrease Pancreatectomy Pancreatic a-amylase Pancreatic dornase Pancreatic elastase Pancreatic hypertrophy Pancreatic lipase Pancreatin [8049-47-6]... 

Thiosulfate cyanide sulfurtransferase symmetry in 78 TTiiouridine 234 Three-dimensional structures of aconitase 689 adenylate kinase 655 aldehyde oxido-reductase 891 D-amino acid oxidase 791 a-amylase, pancreatic 607 aspartate aminotransferase 57,135 catalytic intermediates 752 aspartate carbamyltransferase 348 aspartate chemoreceptor 562 bacteriophage P22 66 cadherin 408 calmodulin 317 carbonic acid anhydrase I 679 carboxypeptidase A 64 catalase 853 cholera toxin 333, 546 chymotrypsin 611 citrate synthase 702, 703 cutinase 134 cyclosporin 488 cytochrome c 847 cytochrome c peroxidase 849 dihydrofolate reductase 807 DNA 214, 223,228,229, 241 DNA complex... 

Fig. 1. Inhibition of porcine pancreatic a-amylase. Substrates, an inhibitor, and their binding orientations in the active site are shown schematically. The arrows denote the catalytic site in each case, (a) The small substrate, G2PNP [17400-77-0] (3) (b) the large substrate, G OH [13532-61 -1] (4) and (c) the inhibitor, 4-phenyl imidazole (5) and the substrate G2PNP (3) in the binding orientation for noncompetitive inhibition. The binding orientation of G2PNP...

Some of the pancreatic enzymes in the lumen include pancreatic amylase, pancreatic lipase, elastase, trypsin, a-chymotrypsin, and carboxypeptidase A. For example, the aspirin derivatives aspirin phenylalanine ethyl ester, aspirin phenyllactic ethyl ester, and aspirin phenylalanine amide have been studied as substrates for carboxypeptidase A [67,68], with the phenylalanine ethyl ester derivative proving to be the best substrate. This study indicated that the carboxypeptidase A may serve as a reconversion site for many drug derivatives. 

Pancreatin is a pancreatic extract usually obtained from the pancrease of slaughterhouse animals. It contains a mixture of enzymes, principally amylase, protease and lipase, and, thus, exhibits a broad digestive capability. It is administered orally mainly for the treatment of pancreatic insufficiency caused by cystic fibrosis or pancreatitis. As it is sensitive to stomach acid, it must be administered in high doses or, more usually, as enteric-coated granules or capsules that may be taken directly or sprinkled upon the food prior to its ingestion. Individual digestive activities, such as papain, pepsin or bromelains (proteases), or a-amylase are sometimes used in place of pancreatin. 

Enzymes that perform the same catalytic function are known as homologous enzymes and fall into two classes. Heteroenzymes are derived from different sources and although they catalyse the same reaction they show different physical and kinetic characteristics. The hydrolytic enzyme a-amylase (EC 3.2.1.1) is found in the pancreatic secretion in man and is different from the enzymes of the same name which are derived from bacteria or malt. Iso-enzymes, sometimes referred to as isozymes, are different molecular forms of the same enzyme and are found in the same animal or organism although they often show a pattern of distribution between tissues. 

Affinity chromatography was carried out on columns prepared with lightly carboxymethylated chitin, which is known to be a poor substrate for lysozyme. Both native lysozyme and regenerated 13-105 were bound to the column at pH 7 and eluted at pH 3. As controls, the basic proteins cytochrome c and pancreatic RNase A, as well as concanavalin A and a-amylase, were not bound from the same solvent at pH 7. These findings constitute a third line of evidence for formation of native-like structure in regenerated 13-105. 

To understand the inhibition of a-amylase by peptide inhibitors it is crucial to first understand the native substrate-enzyme interaction. The active site and the reaction mechanism of a-amylases have been identified from several X-ray structures of human and pig pancreatic amylases in complex with carbohydrate-based inhibitors. The structural aspects of proteinaceous a-amylase inhibition have been reviewed by Payan. The sequence, architecture, and structure of a-amylases from mammals and insects are fairly homologous and mechanistic insights from mammalian enzymes can be used to elucidate inhibitor function with respect to insect enzymes. The architecture of a-amylases comprises three domains. Domain A contains the residues responsible for catalytic activity. It complexes a calcium ion, which is essential to maintain the active structure of the enzyme and the presence of a chloride ion close to the active site is required for activation. 

The reaction mechanism of a-amylases is referred to as retaining, which means that the stereochemistry at the cleaved bond of the carbohydrate is retained. Hydrolysis of the glycosidic bond is mediated by an acid hydrolysis mechanism, which is in turn mediated by Aspl97 and Glu233 in pig pancreatic amylase. These interactions have been identified from X-ray crystallography. The aspartate residue has been shown to form a covalent bond with the Cl position of the substrate in X-ray structure of a complex formed by a structurally related glucosyltransferase. " The glutamate residue is located in vicinity to the chloride ion and acts as the acidic catalyst in the reaction. The catalytic site of a-amylases is located in a V-shaped depression on the surface of the enzyme. 

Amylose, another natural polysaccharide, prepared under appropriate conditions, is not only able to produce films, but is also found to be resistant to the action of pancreatic a-amylase while remaining vulnerable to the colonic flora [82]. However, incorporation of ethylcellulose was necessary to prevent premature drug release through simple diffusion [83], In vitro release of 5-aminosalicylic acid from pellets coated with a mixture of amylose-ethylcellulose in a ratio of 1 4 was complete after 4 hr in a colonic fermenter. By contrast, it took more than 24 hr to release only 20% of the drug under conditions that mimic that of the stomach and of the small intestine. 

Recently 3-dimensional structures for porcine pancreatic a-amylase... 

More specific hydrolysis may be achieved by the use of enzymes. Thus, the enzyme a-amylase in saliva and in the gut is able to catalyse hydrolysis of al 4 bonds throughout the starch molecule to give mainly maltose, with some glucose and maltotriose, the trisaccharide of glucose. Amylose is hydrolysed completely by this enzyme, but the al 6 bonds of amylopectin are not affected. Another digestive enzyme, a-l,6-glucosidase, is required for this reaction. Finally, pancreatic maltase completes the hydrolysis by hydrolysing maltose and maltotriose. 

Monitoring Perform periodic complete blood counts and clinical chemistry tests. Monitor serum amylase levels in those individuals who have a history of elevated amylase, pancreatitis, ethanol abuse, who are on parenteral nutrition, or who are otherwise at high risk of pancreatitis. 

This process is completed in the duodenum where pancreatic a-amylase produces a mixture of monosaccharides, disaccharides, and oligosaccharides. 

The interactions of a-amylases, mainly porcine pancreatic a-amylase, and thiomaltodextrins have been investigated. In 1980, the 3-D structure of porcine pancreatic a-amylase was reported [68], and an analogue of the thiomdtotrio-side (48b), prepared by standard condensation between (34e) and (51c), was effective to label the active site and to identify a second binding site on the siu -face of the protein molecule. 

A few years later, the trisaccharide (48 a) was shown to be a chromogenic substrate for human and porcine pancreatic a-amylase [43 a]. More recently, the use of methyl 4,4 -dithio-maltotrioside (48 c) in further defining the mechanism of action of porcine a-amylase has been investigated [45]. 

Degradation of dietary glycogen by salivary or pancreatic a -amylase. 

The principal sites of dietary carbohydrate digestion are the mouth and intestinal lumen. Salivary a-amylase acts on dietary starch (glycogen, amylose, amylopectin), producing oligosaccharides. Pancreatic a-amylase continues the process of starch digestion. 

Figure 12-6 Drawing showing the overall polypeptide chain fold and relative positioning of the three structural domains of human pancreatic a-amylase. Also drawn are the locations of the calcium and chloride binding sites. Overlaid is the placement of a modified form of the inhibitor acarbose (p. 607) that binds in the active site cleft. MolScript drawing courtesy of G. Sidhu and G. Brayer.

Using the pure anomers of maltose in the same way, we found that crystalline hog pancreatic a-amylase causes the very rapid synthesis of maltotetraose from a-maltose but not from /3-maltose whereas, crystalline sweet potato /3-amylase causes the very rapid synthesis of the same compound, specifically from /3-maltose. Configurational inversion again marks this latter condensation as glycosyl-hydrogen interchange, or glycosyl transfer. 

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