Linkages enzymic hydrolysis

Pacsu4 5 has suggested a structure for starch involving a small number of non-cyclic hemiacetal linkages, the number being presumably sufficient to account for the number of endgroups determined by the methylation method. Halsall, Hirst and Jones6 have commented on this structure, however, and have shown it to be incompatible with the results of periodate-oxidation studies. In addition, these authors pointed out that it would be difficult to explain enzymic hydrolysis and dextrin formation on the basis of such a structure. 

Enzymic hydrolysis is a useful tool for the identification of carbohydrate linkages, as well as for hydrolysis of the (labile) sialic acids. Neeser developed a method wherein the sialic acids are enzymically hydrolyzed and, simultaneously, enzymically converted into stable 2-amino-2-deoxymannose derivatives. This allows determination of carbohydrate constituents of glycoproteins in a single flask. 

The main cyanogenic glycoside in laurel is prunasin, the P-o-glucoside of benzaldehyde cyanohydrin. The enzymic hydrolysis of prunasin may be visualized as an acid-catalysed process, first of all hydrolysing the acetal linkage to produce glucose and the cyanohydrin. Further hydrolysis results in reversal of cyanohydrin formation, giving HCN and benzaldehyde. 

A number of enzyme have been reported to catalyze the hydrolysis of glycosidic linkages in glycoproteins at N-acetylgalactosamine residues, exhibiting specificities at either the a- or the /3-linkage. Enzymes that are reported to act on both a- and /3-linkages have to be clearly characterized as to their specificity. 

Enzymic hydrolysis of dextrans has provided information both on the linkage types and the disposition of different linkages as established by methylation. Since the publication of the earlier article,1 enzymic studies on Leuconostoc dextrans have continued, and investigations of Streptococcus a-D-glucans have shown that there are significant, structural differences between some of these and those of Leuconostoc spp. Reviews on dextrans have appeared.419,420... 

Balousek PJ, McDonough TJ, McKelvey RD, Johnson DC (1981) The effects of ozone upon a lignin model containing the /1-aryl ether linkage Sven Papperstidn 84 R49-R54 Bes RS, Gas G, Molimer J, Vidal P, Mathieu J, Mora JC (1989) Enhancement of poplar cellulose susceptibility to cellulase enzyme hydrolysis by ozonation Ozone Sci Eng 11 217-226... 

Non-cytochrome P450 enzymes may also be involved in oxidative reactions. One such enzyme is alcohol dehydrogenase whose substrates include vitamin A, ethanol, and ethylene glycol. Aldehyde dehydrogenase is another enzyme. Most reduction reactions also involve microsomal enzymes, with the exception of ketone reduction. Nitro compounds are reduced to amines and volatile anesthetics undergo dehalo-genation by microsomal enzymes. Hydrolysis reactions are involved in metabolism of compounds with amide bonds or ester linkages, as in the conversion of aspirin to salicylate (Brown, 2001). 

Experimental evidence for the presence of the /9-linkage in neolactose and celtrobiose is based upon the enzymic hydrolysis of these sugars. Helferich and Pigman r orted that the /9-D-galactosidase component of sweet almond emulsin cleaves neolaetose (4-j8-D-galactosido-D-altrose),... 

D-Fructans are hydrolyzed by two D-fructofuranosidases designated hydrolase A and B.203-205 Enzymic hydrolysis breaks only the ft-D-(2 — l)-linkage between a terminal D-fructofuranosyl group and its adjacent, D-fructofuranosyl chain unit as shown in equation 4. 

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