Similarities in the Action Patterns of Exopolygalacturonate Lyase and Pectinesterase from Clostridium multifermentans

Exopolygalacturonate lyase and pectinesterase from Clostridium multifermentans were assayed simultaneously in the same reaction mixture which contained a highly esterified pectin, polymethyl polygalacturonic acid methyl glycoside. Lyase is specific for unesterified galacturonide residues and cannot degrade this substrate in the absence of the esterase. The rate for esterase was twice the rate for lyase throughout the entire course of the combined reaction. Thus, the molar ratio of the two enzyme activities was the same since the product of the lyase is an unsaturated digalacturonic acid containing two free carboxyl groups. Since clostridial exopolygalacturonate lyase is known to degrade polygalacturonate in a linear manner beginning from the reducing ends of polygalacturonate chains, it was apparent that clostridial pectinesterase must hydrolyze methyl groups in highly esterified pectins with an action pattern similar to that of the lyase. Otherwise it would be impossible for the two enzyme rates to have corresponded on the basis of a 2:1 ratio.     

Effects of calcium, pH, and blockiness on kinetic rheological behavior and microstructure of HM pectin gels

The kinetic behavior during gel formation and the microstructure of 0.75% high methoxyl (HM) pectin gels in 60% sucrose have been investigated by oscillatory measurements and transmission electron microscopy for three comparable citrus pectin samples differing in their degree of blockiness (DB). Ca2+ addition at pH 3.0 resulted in faster gel formation and a lower storage modulus after 3 h for gels of the blockwise pectin A. For gels of the randomly esterified pectin B, the Ca2+ addition resulted in faster gel formation and a higher storage modulus at pH 3.0. At pH 3.5, both pectins A and B were reinforced by the addition of Ca2+. In the absence of Ca2+, the shortest gelation time was obtained for the sample with the highest DB. Microstructural characterization of the gel network, 4 and 20 h after gel preparation, showed no visible changes on a nanometer scale. The microstructure of pectins A and B without Ca2+ was similar, whereas the presence of Ca2+ in pectin A resulted in an inhomogeneous structure.     

Purification and characterization of a new bioscouring pectate lyase from Bacillus pumilus BK2

An alkalophilic bacterium was isolated based on the potential of extra-cellular enzymes for bioscouring. The bacterium was identified as a new strain of Bacillus pumilus BK2 producing an extra-cellular endo-pectate lyase PL (EC 4.2.2.2). PL was purified to homogeneity in three steps and has a molecular mass of 37.3+/-4.8 kDa as determined by SDS-PAGE and an isoelectric point of pH 8.5. Peptide mass mapping by nano-LC-MS of PL revealed 15% homology with a pectate lyase from Bacillus sp. The pectate lyase exhibited optimum activity at pH 8.5 and around 70 degrees C in Tris/HCl buffer. It showed a half-life at 30 degrees C of more than 75 h. Stability decreased with increasing temperature, extremely over 60 degrees C. The enzyme did not require Ca2+ ions for activity, and was strongly inhibited by EDTA and Co2+. PL was active on polygalacturonic acid and esterified pectin, but the affinity showed a maximum for intermediate esterified pectins and decreased over a value of 50% of esterification. The best substrate was 29.5% methylated pectin. PL cleaved polygalacturonic acid via a beta-elimination mechanism as shown by NMR analysis. PL released unsaturated tetragalacturonic acid from citrus pectin and polygalacturonic acid, but did not show any side activities on other hemicelluloses. On polygalacturonic acid PL showed a Km of 0.24 gl(-1) and a vmax of 0.72 gl(-1)min(-1). The applicability of pectate lyase for the bioscouring process was tested on a cotton fabric. Removal of up to 80% of pectin was proven by means of ruthenium red dyeing and HPAEC (65%). Structural contact angle measurements clearly indicated the increased hydrophilicity of enzyme treated fabrics.     

Ca2+-induced down-regulation of Na+ channels in toad bladder epithelium

Regulation of epithelial Na+ channels was investigated by measuring the amiloride-blockable 22Na+ fluxes in apical membrane vesicles, derived from cells exposed to various treatments. Maximal amiloride-blockable 22Na+ uptake into vesicles was obtained if the cells were preincubated at 25 degrees C in a Ca2+-free [ethylenebis(oxyethylenenitrilo)]tetraacetic acid (EGTA) solution. Including 10(-5) M Ca2+ in the cell incubating medium blocked nearly all of the amiloride-sensitive flux in vesicles, even though the Ca2+ was removed before homogenization of the cells. This Ca2+-dependent inhibition of Na+ channels could be induced in whole cells only; incubating cell homogenates with Ca2+ had no effect on the transport in vesicles. The dose-response relationships of this effect were measured by equilibrating cell aliquots with various Ca2+-EGTA buffers, preparing membrane vesicles (in the absence of Ca2+ ions), and assaying them for amiloride-sensitive Na+ permeability. It was found that the Ca2+ blockage is highly cooperative (Hill coefficient of nearly 4) and is characterized by an inhibition constant which varies between 6.4 X 10(-8) to 8.15 X 10(-6)M Ca2+. Thus, it is likely that the above process is involved in the physiological control of Na+ transport. The Ca2+-dependent transport changes were not affected by the calmodulin inhibitor trifluoperasine, vanadate (VO3-), phorbol ester, colchicine, cytochalasin B, 3-deazaadenosine, and 8-bromo-cAMP. Vanadyl (VO2+) ions, on the other hand, produced a "Ca2+-like" inhibition of transport.     

Effects of Ca, Cu, Al and La on pectin gel strength: implications for plant cell walls

Rheology of Ca-pectate gels is widely studied, but the behaviour of pectate gels formed by Cu, Al and La is largely unknown. It is well known that gel strength increases with increasing Ca concentration, and it is hypothesised that this would also be the case for other cations. Pectins are a critical component of plant cell walls, imparting various physicochemical properties. Furthermore, the mechanism of metal toxicity in plants is hypothesised to be, in the short term, related to metal interactions with cell wall pectin. This study investigated the influence of Ca, Cu, Al and La ion concentrations at pH 4 on the storage modulus as a function of frequency for metal-pectin gels prepared from pectin (1%) with a degree of esterification of 30%. Gels were formed in situ over 6 d in metal chloride solution adjusted daily to pH 4. Cation concentration was varied to develop a relationship between gel strength and cation concentration. At similar levels of cation saturation, gel strength increased in the order of La < Ca ? Al ? Cu. The swelling of the gels also varied between cations with Ca gels being the most swollen.     

Effect of polymeric cosolutes on calcium pectinate gelation. Part 3. Gum arabic and overview

Addition of gum arabic (average M_r≈450 kDa; 0.5–2.0 wt%) to solutions of low methoxy pectin (DE 31; 2.0 wt%; pH≈2.9–3.0) with stoichiometric Ca²⁺ caused massive increases in G′ and G″ in the pre-gel state at 90 °C (attributed to segregative interactions promoting formation of calcium-mediated ‘egg-box’ junctions between pectin chains) but had little effect on the gels formed on cooling to 5 °C. This is in marked contrast to the behaviour of other polymeric cosolutes studied in the investigations reported in the two preceding papers, which caused large reductions in gel moduli (attributed to excessive association of calcium pectinate into large aggregated bundles); the difference is tentatively ascribed to strengthening of the calcium pectinate network by divalent counterions to the uronate residues in gum arabic. When the complication of cation exchange was eliminated by extensive dialysis of gum arabic against 100 mM Na⁺ and use of the final dialysate in preparation of mixtures with calcium pectinate, massive increases in G′ and G″ at high temperature were again observed, but with accompanying reductions in moduli at low temperature, which, at gum arabic concentrations above 1.0 wt%, arose from collapse of the developing calcium pectinate network during cooling. The tentative conclusion from this work, and from the two preceding papers, is that enthalpically unfavourable (segregative) interactions between low methoxy pectin and polymeric cosolutes can be relieved in two ways: (i) Ca²⁺-mediated self-association of pectin into compact ordered assemblies which occupy less of the total volume, and (ii) conformational rearrangement of the cosolute molecules to minimise segmental interactions with pectin; conformational rearrangement is inhibited by chain stiffness and by branching; thus polymeric cosolute molecules of limited flexibility are more effective in promoting self-association of pectin than more flexible molecules of comparable size, and branched molecules are more effective than linear chains of comparable stiffness.     

Ultrahistochemical localization of Na+−K+ ATPase,Ca2+-ATPase and alkaline phosphatase activity in a calcium-transporting epithelium of a crustacean during moulting

Summary Periodical changes in Na+–K+-ATPase, Ca2+–ATPase and non-specific alkaline-phosphatase activity were observed using cytochemical techniques in the posterior caeca of the crustacean amphipod, Orchestia cavimana, during the moult cycle. These changes were considered in relation to the calcium transport mechanisms in the posterior caecal epithelium. For both ATPases as well as alkaline phosphatase, the specific reaction products were most intense during the pre-exuvial period, i.e. when calcium is slowly transported against a concentration gradient: the localization of Na+–K+-ATPase activity in microvilli and the upper extracellular channels strongly supports the hypothesis that this enzyme is involved in an indirect, sodium-dependent mechanism for the transport of calcium. The detection of Ca2+-ATPase activity in microvilli would seem to indicate that this enzyme plays a role in the direct, active extrusion of Ca2+ at this level. Although the role of alkaline phosphatase in the transport of calcium remains unclear, the histochemical detection of this enzymatic activity throughout the apical part of the caecal epithelium suggests that this enzyme may be involved in calcium secretion. In post-exuvial period, we found only weak specific reaction products, thus indicating a reduced active calcium transport as these ions are rapidly reabsorbed down the concentration gradient.     

Inhibitory analysis of the monovalent metals' cations interaction with the system of Na+-dependent Ca2+ efflux from the liver mitochondria

Kinetic analysis reveals the mainly competitive inhibition of Na+-dependent Ca2+ efflux from mitochondria by cations of monovalent metals. Potency of the inhibitory effect of metals' cations on Na+-dependent Ca2+ efflux from mitochondria matrix increases in such an order (I50, mM): Cs+ (137.11) < Rb+ (122.63) < Li+ (24.59) < Tl+ (0.541). The results of correlation analysis show that sodium ions translocation by mitochondrial exchanger and its inhibition by the cations of monovalent metals is determined by their affinity for the oxygen-containing ligands and are accompanied with the ions dehydration. Inhibition of the mitochondrial Na+/Ca2+ exchanger by monovalent metal cations is also accompanied with the inhibition of cooperative interactions of metal ions with the ionbinding centers during transport cycle, which can be one of the mechanisms of the inhibition of ions translocation by this ion-transporting system.     

Endo-polygalacturonate lyase of Cytophaga johnsonii

Summary An extracellular endopolygalacturonate lyase of Cytophaga johnsonii was purified from the culture filtrate. It appeared to be homogeneous as judged by polyacrylamide gel electrophoresis at pH 8.6 as well as pH 4.3. The purified enzyme had a pH optimum around 9.0 and required Ca⁺⁺ ions for its maximum activity. The apparent K _mfor polygalacturonic acid was found to be 0.22%. Both paper and column chromatography indicated formation and accumulation of an unsaturated monomer along with unsaturated di-, tri-, tetra- and pentamers from polygalacturonic acid by the enzyme action, indicating that the enzyme cleaved the substrate randomly in a non-hydrolytic manner. The glycosidic linkage next to the non-reducing end of polygalacturonic acid was not resistant to attack by this enzyme unlike in other known polygalacturonate lyases.Abbreviations PG lyase Polygalacturonate lyase - Tris Tris (hydroxymethyl) aminomethane     

Dependence of sodium-calcium exchange current through the membrane of salivary gland cells ofChironomus on pH of the extracellular solution

The dependence of sodium-calcium exchange current (I _Na(Ca)) through the membrane of isolated secretory cells ofChironomus larva on pH of the extracellular solution was studied with the voltage-clamp technique with intracellular perfusion.I _Na(Ca) evoked by hyperpolarization of the membrane from –20 to –60 mV was recorded within physiological values of Na⁺ and Ca²⁺ gradients. It was established that acidification of extracellular solution from pH 7.2 to 4.0 gradually decreased the amplitude ofI _Na(Ca) with pK' — 3.72. In all cases at pH 3.0 an outward current of considerable amplitude emerged in response to membrane hyperpolarization. The reversal of the current occurred at pH around 3.25. A decrease inI _Na(Ca) was due to protonation of acid ionogenic groups (quite possibly, of the residues of aspartic or glutamic amino acids), which had been involved in binding of cations. Alkalization of extracellular solution from pH 7.2 to 10.0 produced a gradual increase in theI _Na(Ca) amplitude; pK' was in the pH range between 9 and 10. The increase inI _Na(Ca) in alkaline medium was probably due to the appearance of negatively charged cations at binding sites, which could be carried by deprotonated thiosulfate groups of cysteine residues. This was indicated by the possibility of initial decrease inI _Na(Ca) under the action of Hg²⁺ ions.Neirofiziologiya/Neurophysiology, Vol. 28, No. 4/5, pp. 193–196, July–October, 1996.     

Enzymatic properties and deduced amino acid sequence of a high-alkaline pectate lyase from an alkaliphilic Bacillus isolate

A high-alkaline pectate lyase (pectate trans-eliminase, EC 4.2.2.2.) from alkaliphilic Bacillus sp. strain KSM-P7, designated Pel-7, was purified to homogeneity. The purified Pel-7 had a molecular mass of approximately 33 kDa as determined by SDS-polyacrylamide gel electrophoresis. The isoelectric point was close to or higher than pH 10.5. In the presence of Ca2+ ions, Pel-7 trans-eliminated polygalacturonate in random manner to generate oligogalacturonides; it exhibited optimal activity at pH 10.5 and around at 60 to 65 degrees C in glycine-NaOH buffer. Mn2+ and Sr2+ ions can serve as cofactors at almost the same level of Ca2+ ions. It also exhibited a protopectinase-like activity, liberating soluble pectin and/or oligogalacturonides from cotton fibers. The pel gene was cloned and sequenced, and the deduced amino acid sequence of mature Pel-7 (302 amino acids, 33, 355 Da) showed some conserved regions in Pel superfamily, although homology to amino acid sequences of known Pels with 27 to 32% identity. Furthermore, Pel-7 appears to have similar core structure of parallel beta-helix and active site topology with other Pels as revealed by secondary structure prediction in the Pel proteins. These results suggest that Pel-7 is basically grouped into Pel superfamily although the enzymatic and molecular properties are different.     

Polygalacturonic acid trans-eliminase of Xanthomonas campestris

Polygalacturonic acid trans-eliminase from the culture fluid of Xanthomonas campestris was purified 66-fold by acetone precipitation, citrate extraction and chromatography on diethylaminoethyl- and carboxymethyl-cellulose. The optimum pH is 9·5 in glycine–sodium hydroxide buffer. Up to 1mm-calcium chloride brings about a remarkable stimulation of the enzyme activity and, at this concentration, no other cations promote or inhibit enzyme action except Ba²⁺ ions, which cause complete inhibition. The enzyme degrades polygalacturonic acid in a random manner; it does not act upon polygalacturonate methyl glycoside, although it can cleave partially (68%) esterified pectin. The end products from polygalacturonic acid at 46% breakdown are unsaturated di- and tri-galacturonic acids, in addition to saturated mono-, di- and tri-galacturonic acids. Pentagalacturonic acid is split preferentially into saturated dimer plus unsaturated trimer, or into saturated trimer plus unsaturated dimer; at a lower rate, it is also split into monomer and unsaturated tetramer. Unsaturated pentamer is split into unsaturated dimer plus unsaturated trimer. Tetragalacturonic acid is split some-what preferentially at the central bond to form dimer and unsaturated dimer, but it is also split into monomer and unsaturated trimer. Unsaturated tetramer is split only at the central bond to yield only unsaturated dimer. Trigalacturonic acid is split into monomer and unsaturated dimer. Unsaturated trimer is cleaved into saturated dimer and probably 4-deoxy-l-5-threo-hexoseulose uronic acid, which has not yet been directly identified. Neither saturated nor unsaturated digalacturonic acid is attacked. The unsaturated digalacturonic acid was isolated and proved to be O-(4-deoxy-β-l-5-threo-hexopyranos-4-enyluronic acid)-(1→4)-d-galacturonic acid.     

Deprivation of Na+, Ca2+ and Mg2+ from the extracellular solution increases cytosolic Ca2+ and stimulates catecholamine secretion from cultured bovine adrenal chromaffin cells

We report here that exposing cultured chromaffin cells to a low ionic strength medium (with sucrose in place of NaCl to maintain osmolarity) can induce a marked elevation in cytosolic Ca2+ concentration ([Ca2+]i) and catecholamine (CA) release. To determine the underlying mechanism, we first studied the effects of low [Na+]o on single cell [Ca2+]i (using fluo-3 as Ca2+ indicator) and CA release from many cells. In a Mg2+ and Ca2+-deficient medium, lowering the external concentration of Na2+ ([Na+]o) evoked CA secretion preceded by a transitory [Ca2+]i rise, the amplitude of which was inversely related to [Na+]o. By contrast, in the presence of either [Ca2+]o (2 mM) and [Mg2+]o (1.4 mM) or [Mg2+]o alone (3.4 mM), lowering the ionic strength was without effect. Furthermore, in a physiologic [Na+]o, [Ca2+]o and [Mg2+]o medium, two or three consecutive applications of the cholinergic agonist oxotremorine-M (oxo-M) consistently evoked a substantial [Ca2+]i rise. By contrast, consecutive applications of oxo-M in a Ca2+-deficient medium failed to evoke a rise in [Ca2+]i after the first exposure to the agonist. To clarify the underlying mechanism, we measured and compared the effects of low [Na+]o and the cholinergic agonists nicotine and oxo-M on changes in [Ca2+]i; we studied the effects of these agonists on both membrane potential, Vm (under current clamp conditions), and [Ca2+]i by single cell microfluorimetry (indo-1 as Ca2+ indicator). We observed that, in the presence of [Ca2+]o and [Mg2+]o, lowering [Na+]o had no effect on Vm. In a Ca2+-deficient medium, lowering [Na+]o depolarized the membrane from ca. –60 to –10 mV. As expected, we found that nicotine (10 M) depolarized the membrane (from ca. –60 to –20 mV) and simultaneously evoked a substantial [Ca2+]i rise that was [Ca2+]o-dependent. However, contrary to our expectations, we found that the muscarinic agonist oxo-M (50 M) also depolarized the membrane and induced an elevation in [Ca2+]i. Furthermore, both signals were blocked by D-tubocurarine, insinuating the nicotinic character of oxo-M in adrenal chromaffin cells from bovine. These results suggest that both nicotine and oxo-M stimulate Ca2+ entry, probably through voltage-gated Ca2+-channels. We also show here that oxo-M (and not low [Na+]o) stimulates phosphoinositide turnover.     

Pectin lyase from Aspergillus sp. CH-Y-1043

Aspergillus sp. CH-Y-1043 synthesizes pectin lyase when grown on citrus pectin at 37° C. Production is favoured by increased esterification degree of the pectin used as carbon source. This enzyme displays higher activity at pH values of 8.5–8.8 and temperatures of 40–45° C. The optimal substrate for the enzyme was highly esterified pectin and no enzymatic activity was registered on polygalacturonic acid. The activity is stimulated by, though not dependent on, divalent cations (Ca²⁺, Mg²⁺, Mn²⁺, Ba²⁺ and Co²⁺) and inhibited by Zn²⁺, and it is not sensitive to the addition of EDTA. The enzyme is very stable when exposed to pH variations: at 4° C it preserves more than 95% of its activity at pHs ranging from 2.0 to 10.0, and at 30° C stability is preserved at pHs ranging from 4.0 to 8.0. At a constant pH of 5.0, the enzyme conserves its stability at temperatures ranging from 4 to 50° C and at pH 8.0 sensitivity to temperature increased. The results on the endo-exo nature of the enzyme suggest that this is an exo-pectin lyase. Correspondence to: G. Aguilar     

Influence of the degree of polymerization of oligogalacturonates and of esterification pattern of pectin on their recognition by monoclonal antibodies

The ability of galacturonic and oligogalacturonic acids with degrees of polymerization (DP) from 2 to 10 to inhibit the recognition of homopolygalacturonic acid by a monoclonal antibody specific for dimers of pectin (F Liners, J-J Letesson, C Didembourg, P Van Cutsem [1989] Plant Physiol 91: 1419-1424) has been tested by enzyme-linked immunosorbent assays. Oligomers of DP9 and above preincubated with the antibodies clearly inhibited the association between the antibodies and immobilized pectin. A minimum DP of nine consecutive galacturonic residues is thus necessary to be associated through calcium cations to form dimers. Randomly deesterified pectin was recognized by the antibody if its degree of methylesterification was <30%, whereas blockwise deesterified pectin was recognized up to 40% of methylesterification. The replacement of calcium ions by magnesium prevented the recognition of polygalacturonic acid by the antibody.     

Microstructure and rheological behavior of pure and mixed pectin gels

The microstructure and the rheological properties of pure HM (high methoxyl) and LM (low methoxyl) pectin gels and of mixed HM/LM pectin gels have been investigated. Gel formation of either the HM or LM pectin, or both, was initiated in the mixed gels by varying the sucrose and Ca(2+) content. The microstructure was characterized by transmission electron microscopy, light microscopy, and confocal laser scanning microscopy. HM and LM pectin gels showed aggregated networks with large pores around 500 nm and network strands of similar character. Small differences could be found, such as a more inhomogeneous LM pectin network with shorter and more branched strands of flexible appearance. LM pectin also formed a weak gel in 60% sucrose in the absence of calcium. A highly inhomogeneous mixed gel structure was formed in the presence of 60% sucrose and Ca(2+) ions, which showed large synergistic effects in rheological properties. Its formation was explained by the behavior of the corresponding pure gels. In the presence of 60% sucrose alone, a homogeneous, fine-stranded mixed network was formed, which showed weak synergistic effects. It is suggested that LM pectin interacts with HM pectin during gel formation, thereby hindering secondary aggregation leading to the aggregated networks observed for the pure gels.     

Conductance and permeation of monovalent cations through depletion-activated Ca2+ channels (ICRAC) in Jurkat T cells.

We studied monovalent permeability of Ca2+ release-activated Ca2+ channels (ICRAC) in Jurkat T lymphocytes following depletion of calcium stores. When external free Ca2+ ([Ca2+]o) was reduced to micromolar levels in the absence of Mg2+, the inward current transiently decreased and then increased approximately sixfold, accompanied by visibly enhanced current noise. The monovalent currents showed a characteristically slow deactivation (tau = 3.8 and 21.6 s). The extent of Na+ current deactivation correlated with the instantaneous Ca2+ current upon readdition of [Ca2+]o. No conductance increase was seen when [Ca2+]o was reduced before activation of ICRAC. With Na+ outside and Cs+ inside, the current rectified inwardly without apparent reversal below 40 mV. The sequence of conductance determined from the inward current at -80 mV was Na+ > Li+ = K+ > Rb+ >> Cs+. Unitary inward conductance of the Na+ current was 2.6 pS, estimated from the ratios delta sigma2/delta Imean at different voltages. External Ca2+ blocked the Na+ current reversibly with an IC50 value of 4 microM. Na+ currents were also blocked by 3 mM Mg2+ or 10 microM La3+. We conclude that ICRAC channels become permeable to monovalent cations at low levels of external divalent ions. In contrast to voltage-activated Ca2+ channels, the monovalent conductance is highly selective for Na+ over Cs+. Na+ currents through ICRAC channels provide a means to study channel characteristics in an amplified current model.     

Immobilization of BSA, enzymes and cells of Bacillus stearothermophilus onto cellulose, polygalacturonic acid and starch based graft copolymers containing maleic anhydride

Poly(maleic anhydride styrene) graft copolymers of cellulose, pectin polygalacturonic acid salt, calcium polygalacturonate, and starch were prepared and used to immobilize proteins. The cellulose grafts coupled quite appreciable quantities of acid phosphatase, glucose oxidase, and trypsin. However, the general retention of activity was somewhat disappointing. Further investigation with acid phosphatase showed that the amount of enzyme immobilized increased as the amount of anhydride in the graft copolymer increased but no such relationship existed for the enzymic activity. The cellulose graft copolymers were hydrolyzed and it appeared that the carboxyl group aided adsorption of the enzyme. Attempts to couple acid phosphatase using CMC through the free carboxyl groups, created by hydrolysis, gave only a small increase in the extent of protein coupling. However, the unhydrolyzed system gave a useful degree of immobilization of cells of Bacillus stearothermophilus, as did a poly(maleic anhydride/styrene)-cocellulose system. Attempts to improve the activity by using grafts based on other polysaccharide supports met with mixed success. Pectin products were soluble. Polygalacturonic acid products were partially soluble and extremely high levels of enzymic activity were obtained. This was probably due in part to the hydrophilic nature of the system, which also encouraged absorption of the enzyme. Attempts were made to reduce the solubility by using the calcium pectinate salt. Immobilization of acid phosphatase and trypsin resulted in inceased protein coupling but relatively poor activities were attained. A starch based system gave similar results. Calcium polygalacturonate was used to prepare an insoluble graft copolymeric system containing acrylonitrile-comaleic anhydride. The resulting gels gave excellent coupling with acid phosphatase which had a very good retention of activity.     

The Ca 2+ pumps and the Na + / Ca 2+ exchangers

The Ca 2+ ATPases or Ca 2+ pumps transport Ca 2+ ions out of the cytosol, by using the energy stored in ATP. The Na + / Ca 2+ exchanger uses the chemical energy of the Na + gradient (the Na + concentration is much higher outside than inside the cell) to remove Ca 2+ from the cytosol. Ca 2+ pumps are found in the plasma membrane and in the endoplasmic reticulum of the cells. The pumps are probably present in the membrane of other organelles, but little experimental information is available on this matter. The Na + / Ca 2+ exchangers are located on the plasma membrane. A Na + / Ca 2+ exchanger was found in the mitochondria, but very little is known on its structure and sequence. These transporters control the Ca 2+ concentration in the cytosol and are vital to prevent Ca 2+ overload of the cells. Their activity is controlled by different mechanisms, that are still under investigation. A number of the possible isoforms for both types of proteins has been detected.© Kluwer Academic Publishers     

Characterization of Two Paenibacillus amylolyticus Strain 27C64 Pectate Lyases with Activity on Highly Methylated Pectin

Two pectate lyases were identified from Paenibacillus amylolyticus 27C64; both enzymes demonstrated activity on methylated pectin in addition to polygalacturonic acid. PelA is in a subclass of the pectate lyase family III. PelB shows some features of pectate lyase family I but is highly divergent.Pectinases have many industrial applications, including uses in food and textile production (9, 12). Additionally, pectinases are important for the degradation of biomass, where pectin can comprise a significant portion of plant structure (5, 6). The degradation of pectin requires methylesterases and depolymerases. Pectin methylesterases are responsible for the hydrolysis of methylester linkages from the polygalacturonic acid (PGA) backbone (24), while pectin depolymerases act upon the polygalacturonate backbone and belong to one of two families, polygalacturonases or lyases. Polygalacturonases hydrolytically cleave the polygalacturonate chain, while lyases cleave by β-elimination, giving a Δ4,5-unsaturated product (10, 19). There are two types of lyases: pectate lyases (PLs), which cleave unesterified polygalacturonate, and pectin lyases, which cleave methylesterified pectin.Paenibacillus amylolyticus strain 27C64, isolated from the larval hindgut of the aquatic crane fly, Tipula abdominalis, possesses a wide range of lignocellulose-degrading enzymes. This study describes two pectate lyases from P. amylolyticus that display unusual activity by combining traits of pectate and pectin lyases (2, 7, 21, 22).