Depolymerizing enzymes

Enzymes depolymerizing polysaccharides may have an endo or an exo action pattern, and may hydrolyze, or cleave by elimination. Both the conformation of the polysaccharide and the active site of the enzyme need to be considered in the enzyme-glycan interaction. endo-Enzymes split, by a random type of depolymerization, glycosidic bonds situated internally in... 

Depolymerizing Enzymes. Depolymerizing enzymes belong to a special class of hydrolases which cleave peptide bonds using water as co-substrate. They are used widely by the topical route as antiinflammatory agents. They reduce inflammation and edema by digesting and dissolving the proteinaceous debris found in inflammatory exudates (179). 

Enzymic depolymerization of juice soluble pectin before it can be deesterified by PE also stabilizes cloud (30). This has been accomplished with pectin lyase (PL), an enzyme which degrades esterified pectin to oligogalacturonic acid esters. 

Converted starches, also called thin-boiling starches, are produced by degradation of the starch chains into small segments. They can be cooked in water at higher concentrations than native starches. Low-viscosity starches are needed in applications where a high solid starch paste with a pumpable and workable viscosity is required. There are four classes of commercial converted starches dextrins (hydrolysis in solid-state) acid-modified starches (hydrolysis in a slurry) oxidized starches and enzymically depolymerized starches. 

Enzyme activity may be enhanced by a chemical pretreatment, as in the example of alkaline hydrogen peroxide on corn fiber, where the hydrolytic rate was increased by a factor of 1.6 (Leathers, 1993). Some enzymes depolymerize polysaccharides by 3-elimination. 

The reverse of sulfation is desulfation, which can be effected under mild enzymic conditions [96]. Similarly, enzymic depolymerization, closely guarded by trade secrets, is routinely used in the production of heparin-derived dmgs. 

Commercial LMWHs have average molecular weight (A/r) of 2500-8000. They are prepared either by size fractionation, or (now prevalently) by chemical or enzymic depolymerization of heparin. Most common manufacturing processes of... 

The enzyme system which catalyzed the incorporation of uridine 5-(n-glucopyranosyl pyrophosphate) and uridine 5-(D-glucopyranosyluronic acid pyrophosphate) into Sill had a pH optimum at 8.35 and a temperature optimum at 32 , and was dependent upon Mg . The synthetic system was present in the particulate fraction which sedimented between 30,000 and 100,000 g. The activity of the enzyme appeared to depend on the presence of preformed Sill and was stimulated by the addition of oligosaccharides, containing 8 to 12 disaccharide units, which were obtained by brief enzymic depolymerization of Sill. Smaller oligosaccharides, of the form D-glucosyluronic-(l—>4)-D-glucose (n = 1, 2, and 4) showed no... 

Aphids have flexible, stylet-like mouthparts adapted for probing of plant tissues. By this means, the aphid must use chemical cues from the plant to determine if the plant is a suitable host (host plant quality), where the aphid is on the plant, the location of the stylet within the plant tissues, and the direction to probe to locate the plant phloem (Campbell and Dreyer, 1990 Dreyer and Campbell, 1987). Aphids avoid many of the toxic compounds stored in plant cells by probing between the cell walls. These insects are able to penetrate the intercellular spaces by producing a variety of digestive enzymes which depolymerize the pectins and hemicelluloses forming the intercellular-cell wall matrix. Aphid-host plant compatibility is associated to the extent that these enzymes depolymerize their respective substrates, and a reduced rate of depolymerization is often associated with host plant resistance. Differences in methoxylation, acetylation, or neutral sugar composition in the matrix polysaccharides are often involved in this reduced depolymerization. Further, specific breakdown products from depolymeri-... 

Acetyl-CoA carboxylase is also inhibited by long-chain fatty acyl-CoA, and such inhibition is accompanied by enzyme depolymerization (91, 92, 95). Binding of 1 mole of palmityl-CoA per mole of rat liver acetyl-CoA carboxylase inhibits the enzyme (95). The Ti for palmityl-CoA, about 5 nM, is far lower than the critical micellar concentration of the thioester this indicates that the inhibition may be physiologically significant. If the allosteric control mechanisms of citrate promoted "substrate activation or fatty acyl-CoA mediated "feed back inhibition of fatty acid synthesis function at all under in vivo conditions, they must function as a dual mechanism (90). 

In addition, it has been observed that the phosphorylation of the carboxylase in vitro also causes enzyme depolymerization 71, 105). 

Lee and Kim reported that carboxylase species from rat epididymal fat tissues which had been treated with epinephrine sedimented more slowly than enzyme from control tissues the sedimentation constants were identical to those of the protomers and the intermediate species (67). Halestrap and Denton (39) observed similar hormonal effects by measuring the amount of sedimentable carboxylase under different conditions. In further studies of the slow sedimenting carboxylase by immunochemical and kinetic methods, Lee and Kim showed that the enzyme species from hormone-treated tissues were not simply depolymerized, but were intrinsically inactive species of the carboxylase (67). Such studies, together with the demonstration that epinephrine inactivation of the carboxylase is due to phosphorylation (6S), establish that phosphorylation causes enzyme depolymerization and that depolymerized enzjmes are the phosphorylated forms and not protomers of unphosphorylated species. Thus the studies discussed above show the close relationship between covalent phosphorylation and the quaternary structure of the carboxylase and also the occurrence of such a relationship under both in vivo and, in vitro conditions. 

The properties and modes of action of cellulases and technological aspects of the enzymic depolymerization of cellulosic materials have been discussed. 

Hultin (77) has derived an expression for the enzymic depolymerization of hyaluronic acid based on Staudinger s (182) equation relating specific viscosity and molecular weight. This equation permits the calculation of a microunit for enzymic activity. The formula was applied to data published by Madinaveitia and Quibell (112) and Swyer and Emmens (183). The values obtained showed fairly good agreement for the higher substrate concentrations. 

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