Calcium pectate

Pectin belongs to a family of plant polysaccharides in which the polymer backbone consists of (1— 4)-linked a-D-galacturonic acid repeating-units. Often, (1— 2)-linked a-L-rhamnose residues interrupt the regular polygalacturonate sequence. The high viscosity and gelling properties of pectins are exploited by the food and pharmaceutical industries. X-Ray studies on sodium pectate, calcium pectate, pectic acid, and pectinic acid (methyl ester of pectic acid) have disclosed their structural details. 

Calcium Pectate. Calcium pectate was prepared from the calcium pectinates by the method of Emmett and Carre (5) in amounts ranging from approximately 89 to 96%. The alcohol-precipitated products, prepared under similar conditions (17), ranged from approximately 72 to 90%. Hinton (7) has shown that calcium pectate can be used as a measure of the purity of a pectin. 

Calcium is important in the growth of meristematic tissues including both shoot and root tips. It frequently accumulates in cell walls and leaves in the form of calcium pectate. Calcium also apparently acts as an activator for certain enzymes and performs other metabolic functions that are not yet clearly defined. It seems to neutralize to some extent the undesirable effects of nutrients in the plant that are either undesirable or absorbed in improper amounts or ratios. Too much calcium may, however, depress the uptake of potassium and magnesium, but unlike these elements it is comparatively immobile in the plant. 

Calcium hyaluronate, 376-377 Calcium pectate, 353 Calcium welan, structure, 432-434 Candida utilis, thiamine synthesis,... 

In our investigations, we also detected the sorption of isoPO from potato, Arabidopsis and wheat, by calcium pectate. Moreover, we observed the binding with calcium pectate of potato PO from the fraction of proteins ionically bound with cell walls. It is likely that the ability of some PO isoforms to bind with pectin ensures the spatial proximity of these enzymes to the sites of the initiation of lignin synthesis and that these "pectin-specific" isoforms take part in this process. 

In contrast, observation of the c.d. with the addition of Ca(OH)2, as a function of d.p., demonstrated that terminal and central units react differently towards Ca ". This is illustrated in Fig. 27 for the dimer and the polymer. Again, the intensity of the c.d. band decreases as the polymer binds calcium and begins to gel. Results for both salt forms are attributed to a helix having a two-fold screw-symmetry, in analogy with calcium pectates. The gelling would then involve a multi-chain association, with crosslinking by the calcium ions to form an egg box structure. ... 

The rheological behaviour in the range of LM pectin was analyzed and the sol-gel diagram established [59] for different stoichiometric ratios. In their paper, these authors determined the gel times for sodium pectate during calcium-induced gelation and the variation of the gel time with polymer concentration, stoichrometric ratio and temperature. 

At end, it is important to mention that calcium pectate gel beads were compared with calcium alginates gel beads for all entrapment uses [65, 66] in this work, the authors determined the pore size of the beads by size exclusion chromatography using dextran standards and other solutes. 

Figure 7. The egg-box structure for the junction zones of dilute calcium pectate gels two galacturonan chains in the twofold (2i) helical conformation with calcium ions (shaded circles) locked between them.

Figure 8. The Walkinshaw Amott model [46] for solid calcium pectate, with the galacturonan chains in the right-handed (ii) helical conformation.

Figure 9. The cable model for the structure of concentrated calcium pectate gels. Egg-box dimers link single-chains segments (top left) and are themselves ed together by larger aggregates of either egg-box or 3i helical chains (lower right)...

F ure 10. solid-state NMR spectra of calcium pectate in the solid (A) and gel (B) forms. Inset resolution-enhanced spectra. The gel concentration was 290 g/1. 

Thus pectins in muro contain most elements of the cable model but have additional features due to esterification (acetyl- as well as methyl-) and branching. The ionic junction zones are similar to those of calcium pectate gels in vitro but also contam methyl-esterified junctions, and most of the single chains probably have a relatively high degree of methyl-esterification. 

Figure 12. Binding of calcium ions by pectate and apple pectin, measured by equilibrium dialysis gainst citrate to buffer the concentration of free calcium ions at low levels.

There is strong evidence that PE-pectate complexes exist within the cell wall as well as in plant extracts. The formation of these complexes and release by cations and/or cell wall potential is thought to influence cell wall growth and extension (16, 17). The data in Fig. 1 and Fig. 2 depicts the effect on PE activity of calcium or ferric chloride and the effect of the... 

Lips A., Clark A.H., Cutler N. Durand D. (1991) Measurement of cooperativity of binding of calcium to neutral sodium pectate. Food Hydrocolloids 5,87-99. 

The r2 isolate of Fusarium oxysporum f. sp. radicis-lycopersici (FORL) produced several pectic enzymes that differ in substrate preference, reaction mechanism, and action pattern. We have detected three forms that have lyase activity, an absolute requirement for calcium, and pis of 9.20, 9.00 and 8.65. The two most alkaline forms had a weak preference for pectin whereas the other was more active on pectate. The three lyases were produced when the fungus grew on pectin and on restricted galacturonic acid (data presented in the "XV Congreso Nacional de Microbiologia" [21] and sent for publication). 

The enzyme had a requirement for calcium. The addition of EDTA to the reaction mixtures, resulted in complete loss of activity, whereas the addition of CaCl2 increased the activity (figure 8). Presumably, sufficient contaminating calcium ions were present in the dialyzed enzyme and substrate mixture to permit the limited activity of the controls, but apparently these were removed by chelation with EDTA. The optimum concentration was in the range of 5 to 15 M, and higher concentration resulted in a decrease in activity. Phoma medicaginis var. pinodella synthesizes a pectin lyase that lacked an absolute requirement for calcium ions but maximum enzyme activity required the presence of 1 mM Ca [25]. The lyase from Fusarium solani f sp. phaseoli, that is active on pectin and pectic acid, is calcium-dependent [30]. Most of the pectate lyases characterized are calcium-dependent the pectate lyase from Rhizoctonia solani [34] and the endopectate lyase fi om Fusarium solani f sp. pisi [31]. 

As previously described [2, 11], E. chrysanthemi possesses at least seven pectate lyases. Among them, PelZ seems to belong to a new family. However, its biochemical characteristics, basic optimal pH, calcium dependence and methylation sensitivity corroborate with those of the other pectate lyases of E. chrysanthemi. The weak expression of the pelZ gene and the weak activity of the PelZ protein seem to be correlated with specific environmental conditions. PelZ may act on pectin in synergy with the major pectate lyases. 

Macmillan and coworkers51 105 106 purified pectinesterase produced by Clostridium multifermentans by using practically all of the available methods and materials (calcium phosphate gel, DEAE-cellulose, DEAE-, QEAE-, CM-, and SE-Sephadex, Sephadexes G-75, G-100, G-150, and G-200, Sepharose 4B, and zonal centrifugation). However, they could not separate pectinesterase from exo-pectate lyase, and, hence, they postulated that either (a) a complex of the two enzymes having an apparent molecular weight of 400,000 exists, or (b) the two enzymes are identical in their molecular species. On the basis of the mode of action of this pectinesterase in comparison with that of those from tomatoes and from Fusarium ox-ysporum, the existence of a complex of pectinesterase and exopectate lyase in Clostridium multifermentans appears to be the more probable. 

The development of modem separation techniques has affected the purification procedures employed for D-galacturonanases. Fractional precipitation with ammonium sulfate and with organic solvents are now used only in combination with new separation techniques. To separate fractions having D-galacturonanase activity, adsorption to pectate or calcium pectate gel has been used in several instances.157-207... 

Adsorption on calcium pectate and calcium phosphate, and chromatography on DEAE-cellulose, were used for the purification of pectin lyase from Aspergillus fonsecaeus.253 Two forms of pectin lyase (having pH optima at 7.3 and 8.3) were isolated266 from the culture filtrate of Sclerotinia fructigena by chromatography on Seph-adex G-75 and CM-Sephadex C-50. 

In bean hypocotyl, the increase of resistance in the course of ripening was found to be accompanied292 by a decrease in the meth-oxyl content from 0.5 to 0.2%, while the content of calcium increased from 0.38 to 1.92%. An increased content of calcium was observed in a resistant variety of cucumber hypocotyl.293 These results suggest that one of the protective mechanisms of the plant against infection is the conversion of pectic acid into calcium pectate, which is resistant to the action of pectic enzymes. 

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