Deesterification

Niehaus, W.J., Jr (1978). A proposed role of superoxide anion as a biological nucleophile in the deesterification of phospholipid. Bioorganic Chemistry, 7, 77-84. 

Fig. 10. Intercellular junction zones of carrot cells grown in suspension have been observed in electron microscopy after immunogold labeling with the 2F4 antibody, (a) no treatment of the sections prior to labeling the gold particles are restricted to the center of the junction zones (b) enzymatic (pectin methyl esterase) deesterification of the E.M. grids before labeling the deesterified pectins present in the primary walls now bind the probe. Scale bars = 1 pm.

When cell-wall fragments are incubated in molar NaCl, ionically bound proteins are released into the incubation medium. All investigated crude cell extracts deesterified Citrus pectin (Table 2) but the deesterification rates were clearly higher when the enzymes were still bound to the cell walls, indicating a major loss of activity during the solubilization process. 

The activity of PE was measured [25] from the increase of carboxylic groups during the pectin deesterification (5 g/L) in phosphate-citrate buffer 50 mM, pH 4.7. Continuous titration of the reaction mixture with NaOH 0.01 M was employed for product determination. 

Qualitatively, the results observed with ferric chloride and lead acetate were highly variable. It was first noted with ferric chloride that gels were forming within the reaction vessel We observed the formation of translucent gels in the reaction vessel with calcium chloride, spermidine and ferric chloride. In the case of lead acetate, a feathery type precipitate formed in the reaction vessel. Macdonald et al. (14) observed formation of a clear gel and flocculated precipitate in high ester pectin treated with lemon endocarp and peel PE isozymes, respectively. They hypothesized that the different gel structures were due to unique mechanism of deesterification by the PE isozymes. Our results with different cations and formation of different gel structure or precipitate seems to be similar to that reported by Macdonald et al. (14). If there is a different mechanism of de-esterification for plant PEs,... 

DM and DAc of various pectin fractions except those of OHSP (due to deesterification during extraction) are summarized in Table 5. The DM of WSP of conventionally canned carrots did not significantly differ from that of fresh carrots,while in the presence of CaCk a considerable increase was observed. This increment can be ascribed to cross-Unking of water soluble-low methylated... 

The deesterification of pectin with ammonia has industrial application because of the following reasons ... 

There are not many publications in the specialised literature examining the deesterification in the presence of mineral salts. 

R.M.McCready et al.[l] demonstrate that the adding of O.IM NaCl to 0.33 M ammonia hydroxide enhances the deesterification more than twice. The adding of other chlorides, such as KCl, MgCb and CaCb also enhances the reaction. The effectiveness of the ions in relation to the deesterification and rate constant is arranged in the following order Ca>Mg>Na, K. The equal values of pH and ion strength prove that only the specific cation effect is responsible for the enhanced velocity. 

Reistma et al. [2] establish the positive influence of NaCl on the deesterification of ester groups of amidated pectins with ammonium hydroxide, without discussing the mechanism of the catalytic action of the sodium chloride. 

The degree of deesterification Rd shows the percentage of the initial ester groups participating in the deesterification. 

From the degree of transformation - expressed by the relative change of each type of carboxyl group Rd (degree of deesterification), Rh (degree of hydrolysis) and Ra (degree of ammonolysis). 

It may be noted from the data for Rd (Table 1) that at the conditions chosen by us for performing of deesterification with ammonia a degree of transformation above 80 % is reached. Both competitive reactions of hydrolysis and ammonolysis are commensurable in regard of their rate. This fact is very favourable for investigating cations influence on the course of the deesterification and the rate of the investigated competitive reactions(3), (4) and (5). 

Influence of the Monovalent Ions. The addition of ammonium salts retard the course of the deesterification by changing the reaction rate of hydrolysis and ammonolysis. By increasing the concentration of the ions the conversion of the ester groups is reduced from 83.3 % for 0,01 M to 62.8 % for 0.2 M (without added salt this value is 84.05 %), and the ratio hydrolysis ammonolysis is changed correspondingly from 53.8 76.2 to 37.3 62.7 (without added salt this ratio is 57.6 42.4). 

The behaviour of the added alkali cations is different. Na and K enhance the deesterification and the differences in the interaction of both cations at the separate reactions are inessential. The use of these ions in the deesterification of highly esterified pectin in either enzyme or chemical method shows that they only enhance the hydrolysis. Since in the investigated case they cannot influence the equilibrium (6), the enhancement of the hydrolysis leads to faster exhausting of the reactable -COOCH3 groups and thus is reduced the rate of the competitive ammonolysis. 

Considering only this equation, it could be suggested that in the model systems when MgCb is added, the deesterification is retarded because of the reduction of both concentrations - first of OH, due to the formation of Mg(OH)2, and second, of NH3, due to the shifting of the equilibrium (6) to the right. 

It is clear that this changes on the cell wall must have important consequences on the firmness of the fruit. The breakdown of linkages between pectic polysaccharides and the matrix is likely to be an important factor on the irreversible loss of firmness. The deesterification of polysaccharides, on the other hand could have an effect of increasisng firmness. There is, however, another factor that should be taken into account, the alcali deesterification of the... 

The two most striking features of these time-courses are that, though the initial speed of the reaction increases markedly with the pH, the final level does not, as the reaction stops much earlier. This was not due to a drop of pH below the values suitable for P-elimination, as the pH change were slight (-0.2 at pH 11, no measurable change at pH 9). In order to check wether this plateau was due to disparition of suitable reaction sites, i.e. methoxylated galacturonic acid residues, we have investigated in detail the deesterification reaction. 

The deesterification reaction, or more precisely the demethylation reaction, was followed by measuring the amount of methanol liberated (Fig. 2). 

This study reports on the production of pectic enzymes and partial characterization of polygalacturonases produced by Candida boidinii. Candida boidinii belongs to the so called methylotrophic yeasts with famous utilization of methanol. Pectin, the natural substrate of pectic enzymes complex, can serve for microorganisms as a C - source by two different ways after deesterification with pectinesterase as methanol and after hydrolytic cleavage with... 

Enalaprilat and SQ27,519 are angiotensin-converting enzyme (ACE) inhibitors with poor oral absorption. Enalapril and fosinopril are dipeptide and amino acid derivatives of enalaprilat and SQ27,519, respectively [51] (Fig. 10). Both prodrugs are converted via deesterification to the active drug by hepatic biotransformation. In situ rat perfusion of enalapril indicated a nonpassive absorption mechanism via the small peptide carrier-mediated transport system. In contrast to the active parent, enalapril renders enalaprilat more peptide-like, with higher apparent affinity for the peptide carrier. The absorption of fosinopril was predominantly passive. Carrier-mediated transport was not demonstrated, but neither was its existence ruled out. 

Deep-ultraviolet chemically amplified resists, 15 163-181 Deepwater barges, 25 327 Deep-well turbine pumps, 21 68 Deesterification, of aspartame, 24 227 DEET, 2 549t Defaunation, 10 871 D,E,F color scale, 7 310 Defect Action Levels (DALs), 23 160 Defects, in silicon-based semiconductors, 22 232... 

Scheme I Acid-catalyzed deesterification of DMBZMA copolymers.

Scheme II Thermal and acid-catalyzed deesterification of polymethacrylates.

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