Limited Depolymerization Research Articles

Exploration of the regulatory mechanism of pulsed electric field on the aggregation behavior of soybean protein isolates

As an emerging protein modification technology, pulsed electric field (PEF) technology in modifying soybean protein isolates (SPI) suffers from unclear mechanism and controversial changes in aggregation structure. To address these issues, the effects of PEF treatment with different electric field intensities (5–30 kV/cm) on the aggregation behavior and spatial structure of SPI were investigated. The results showed that the SPI aggregates exhibited a trend of depolymerization followed by reaggregation with the increase of PEF intensity. At 10 and 15 kV/cm, the polarization effect of PEF induced the unfolding of the tertiary structure of SPI, leading to the enhancement of the electronegativity of the side chains, and the electrostatic repulsive force between the molecules promoted the depolymerization of SPI aggregates. However, with the withdrawal of PEF, the structure of the SPI was partially reversible, resulting in a limited depolymerization effect. When the PEF intensity reached 20 kV/cm and above, SPI underwentstructure unfolding, subunit dissociation, continuous exposure of hydrophobic groups and sulfhydryl groups, and ultimately reaggregation mediated by hydrophobic interactions and disulfide bonding, resulting in the formation of high molecular weight soluble and insoluble protein aggregates. In addition, the formation of free radicals under strong electric fields (≥20 kV/cm) accelerated the oxidation of SPI and promoted the rapid formation of disulfide bonds. This study provides a theoretical basis for the targeted regulation of SPI aggregation structure by PEF.

New insights on the degradation of polystyrene and polypropylene by larvae of the superworm Zophobas atratus and gut bacterial consortium enrichments obtained under different culture conditions

This study aims to deepen knowledge of the biodegradation of plastics, focusing on polypropylene (PP) fabric from surgical masks and polystyrene (PS) by larvae of Zophobas atratus as well as of specialized bacterial consortia from their gut, which were obtained in different enrichment conditions (aerobic, anaerobic, presence or absence of combined nitrogen). Plastics ingested by larvae obtained in Spain did not show any signs of oxidation but only limited depolymerization, preferably from the lowest molecular weight chains. Gut microbiota composition changed as an effect of plastic feeding. Such differences were more evident in bacterial enrichment cultures, where the polymer type influenced the composition more than by culture conditions, with an increase in the presence of nitrogen-fixers in anaerobic conditions. PS and PP degradation by different enrichment cultures was confirmed under aerobic and anaerobic conditions by respirometry tests, with anaerobic conditions favouring a more active plastic degradation. In addition, exposure to selected bacterial consortia in aerobiosis induced limited surface oxidation of PS. This possibly indicates that different biochemical routes are being utilized in the anaerobic gut and in aerobic conditions to degrade the polymer.

Cell wall disassembly events accompanying softening in the core and external zones of the strawberry fruit receptacle

Softening is one of the most important changes determining the quality and postharvest life of strawberry. Though some studies have characterized the cell wall modifications accompanying firmness loss during storage, the reports on polysaccharide disassembly are widely variable and in some cases contradictory. To further understand strawberry postharvest softening, conducted a comprehensive cell wall analysis including polymer solubilization, depolymerization and composition of the Core and External zones of fruit´s receptacle during storage. Core tissues were firmer and stiffer and softened more than the External receptacle zone. Wall dismantling was remarkably different depending on the region evaluated. Core tissues showed greater losses and size downshift of hemicelluloses as well as more extensive depolymerization of pectin. Instead, softening in the External region occurred with limited depolymerization and with massive loss of arabinose and xylose. Xyloglucans showed active turnover in the Core, whereas xylans were the most degraded hemicelluloses in the External region. Results show that each discrete region of the strawberry fruit receptacle has a unique sequence of biochemical wall dismantling events leading to postharvest softening.

Reaction behavior of milled wood lignin in an ionic liquid, 1-ethyl-3-methylimidazolium chloride

We investigated the reaction behavior of milled wood lignin (MWL) obtained from Japanese cedar (Cryptomeria japonica) and Japanese beech (Fagus crenata) in an ionic liquid, 1-ethyl-3-methylimidazolium chloride ([C2mim][Cl]). This solvent can liquefy wood. The sample was treated with [C2mim][Cl] at 120 °C using an oil bath or microwave irradiation. MWL easily dissolved in [C2mim][Cl]. Although solubilized, MWL was slightly depolymerized and it retained its high molecular weight after 96 h of treatment. Only small amounts of low molecular weight compounds such as vanillin, coniferylaldehyde, syringaldehyde and sinapylaldehyde were produced. As the treatment time was extended the chlorine from [C2mim][Cl] reacted with the MWL. These results indicate that MWL is stable in [C2mim][Cl] although limited depolymerization and modification by [C2mim][Cl] occurred.

End‐group rearrangements in poly(propylene sulfide) matrix‐assisted laser desorption/ionization time‐of‐flight analysis. Experimental evidence and possible mechanisms

Polysulfides [poly(1,2-alkylene sulfides)] are oxidation-responsive polymers that are finding application in drug release and biomaterials. The precise knowledge of their macromolecular characteristics is of the essence in view of their application to biological systems. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) with and without silver trifluoroacetate was used to characterize a series of polymers with increasing molecular weight in the range 1000-4000 g/mol and with low polydispersity (<1.12). Well-resolved peaks and accurate mass-measured values were obtained using a 2-(4-hydroxyphenylazo)benzoic acid (HABA) matrix, but significant fragmentations took place in the absence of silver as a cationizing reagent. Elimination reactions appeared to occur at terminal groups and limited depolymerization could be recorded. Interestingly, the most common fragmentation pathway seemed to be based on an as-yet-unreported process of hydrogen transfer requiring the presence both of ester groups and of thioethers. The use of an appropriate cationizing reagent (silver trifluoroacetate) appeared to suppress end-group eliminations; we hypothesize that this action is based on the involvement of the terminal groups in silver chelation.

Cell wall modification during development of mealy texture in the stony-hard peach “Odoroki” treated with propylene

The melting peach cultivar “Akatsuki” [ Prunus persica L. Batsh] develops melting texture during ripening, but the stony-hard peach cultivar “Odoroki”, softens and develops a mealy texture when treated with propylene. Cell wall polysaccharides were fractionated as 1,2-diaminocyclohexanetetraacetic acid (CDTA)-, Na 2CO 3-, NaOH-soluble fractions, or the cellulosic residues that remained after solvent extraction. Size-exclusion chromatography of the CDTA-soluble fraction revealed a limited depolymerization of polyuronides in mealy “Odoroki” fruit, accompanying a lower level of endo-polygalacturonase (endo-PG) and a higher level of exo-PG activities compared to melting “Akatsuki” fruit. “Akatsuki” fruit showed increases in the arabinose, galactose and rhamnose contents in the CDTA-soluble fraction. These neutral sugars decreased in the Na 2CO 3-soluble and cellulosic residue fractions during ripening. Similar changes were observed for neutral sugars other than arabinose during softening in mealy “Odoroki” fruit. Arabinose content did not increase in the CDTA-soluble fraction of “Odoroki” fruit; however, arabinose content decreased in the Na 2CO 3-soluble fraction and in the cellulosic residue as observed for “Akatsuki” fruit. A significant increase in α- l-arabinofuranosidase activity, about 10 times higher than for “Akatsuki” fruit, was observed in propylene-treated mealy “Odoroki” fruit. Differences in ripening-associated metabolic changes in the cell walls of these peach cultivars seem to be related to their differences in texture.

An efficient procedure for studying pectin structure which combines limited depolymerization and 13C NMR.

A protocol for partial thermally-induced depolymerization of differently methoxylated pectin samples is described. The resulting macromolecules have been fully characterized with various complementary techniques, such as size exclusion chromatography (SEC), potentiometry, viscometry and 13C NMR. Optimum conditions afford samples at 50-80% yield with weight-average molecular weights in the 4 to 20 kDa range. The major fraction of these polysaccharides adopts the random-coil conformation and such samples are suitable for 13C NMR structural studies at room temperature. The methoxyl distributions of two apple pectin samples with a degree of esterification (DE) between 54 and 74% and a citrus pectin (DE, 72%) were shown to be random in nature, whereas that of a lightly methoxylated apple pectin (DE 39%) was partially blockwise. The carbon relaxation parameters of the depolymerized pectins attain asymptotic values for Mw > 4 kDa. The Mw values estimated from intrinsic viscosity data with the Mark-Houwink relationship reported for native pectins are in good agreement with those obtained by either end-group analysis (NMR) or SEC. Thus, all the physicochemical data indicate that the secondary structure of the isolated chains of depolymerized pectin is closely related to that of the parent polymers. Finally, pectinmethylesterase activity towards the depolymerized pectins was similar to that of the untreated samples.

Purification of ferulic acid by adsorption after enzymic release from a sugar-beet pulp extract

An aqueous sugar-beet pulp extract obtained by pressure-cooking and mainly composed of pectic fragments, was treated with a pectinolytic preparation. A strong, but limited depolymerization occurred fastly, while feruloyl-esterase activities appeared more gradually, pointing to some deficiencies of the enzymic mix. The solubility of ferulic acid in the sugar-rich, acidic hydrolysate proved stable, and no crystallization could be triggered in this complex medium. Comparative batch tests were carried out with preselected, commercially-available adsorbents: activated carbons, polystyrenic divinylbenzene-crosslinked resins, and polyvinylpolypyrrolidone (PVPP). In each case, the ferulic acid uptake is lower at pH values above 4.5, the pKa determined for its carboxylic group. The natural acidity of the hydrolysate, pH 3.4, was chosen as the optimum. The chemically-activated carbon (SA1817) has the highest affinity for ferulic acid, while Amberlite XAD-16 performs best among the polystyrenic resins. PVPP also offers an appreciable adsorption efficiency. Selectivity is ensured, since only the charcoal removes a slight amount of galacturonic acid, which is released on rising the pH to 4. Alkaline dissociation and ethanolic extraction were investigated as desorption strategies, and ethanol was kept as the most suitable common eluent. Dynamic column studies allowed to estimate the maximum specific capacity at about 22, 12 and 8% (w:w ferulic acid/adsorbent) for the chemical granular activated carbon (GAC), XAD-16 and PVPP, respectively. Ferulic acid is quantitatively recovered after ethanolic elution of the three selected adsorbents, and the best purity is achieved with PVPP, followed by GAC.

Molecular Mass Changes in Cell Wall Pectins of Tomato Fruit Locule Tissue in Response to Deesterification

Changes in the gel filtration behavior (apparent mol mass) of cell wall pectic polymers have been observed in a number of ripening fruits, including some that express little or no detectable polygalacturonase (PG). Pectins from tomato (Lycopersicon esculentum, Mill. v. Solar Set) fruit locule tissue show limited depolymerization during ripening, although alkali-soluble polymers are of reduced mol mass relative to water- and chelator-soluble polymers (Plant Physiol. 111:447). This study addressed whether the lower mol mass of alkali-soluble polymers was a consequence of extraction or specific metabolism of these wall polymers. Pectins from sequential water and chelator extractions of ethanol-insoluble solids from mature green tomato locule tissue were subjected to alkaline conditions. The size distribution of both water- and CDTA-soluble pectins treated with weak alkali were downshifted and similar to those extracted directly by weak alkali, indicating structural similarities of the three pectin fractions. Spectrophotometric analysis showed no involvement of β-elimination hydrolysis in the apparent mol mass reduction. The alkali-treated polymers were of greatly enhanced susceptibility to PG-mediated degradation. The alkali-associated changes also occurred in response to pectinmethylesterase hydrolysis. The results indicate that deesterification can strongly influence gel filtration behavior of pectins and may explain the apparent mol mass decreases of pectins in fruits not containing PG.

Inhibitory effects of PG‐H/aggrecan and PG‐M/versican on avian neural crest cell migration

Aggrecans and PG-M/versicans represent two newly defined families of hyaluronan-binding proteoglycans for which the function is still poorly understood. Using the avian neural crest as a model system, we have examined the molecular mechanisms entailed in the cell-proteoglycan interaction during embryonic cell motility. Both the primary cartilage aggrecan of the avian embryo (PG-H/aggrecan) and the largest variant of the avian mesenchymal versican (PG-M/versican VO) failed to support neural crest cell adhesion and migration when topographically immobilized onto the substrate. Conversely, solely the PG-H/aggrecan, and similar aggrecans from other species, counteracted the migration-promoting effect of a number of matrix molecules lacking proteoglycan affinity. This inhibitory effect was not reproduced by the isolated glycosaminoglycan chains, the isolated core protein, the reduced and alkylated macromolecule, or the aggrecan in which the G1 hyaluronan-binding domain had been inactivated with hyaluronan fragments or antibodies. Limited depolymerization of the side chains and preincubation of the PG-H/aggrecan with anti-glycosaminoglycan antibodies differentially reduced the inhibitory activity of the proteoglycan on cell motility. The results demonstrate a diverse inhibitory effect of aggrecans and PG-M/versicans on embryonic cell movement and show that the inhibitory action of aggrecans is independent of substrate binding, is dependent on a G1 domain-mediated association of the intact proteoglycan with cell surface-bound hyaluronan, and is differentially mediated by its glycosaminoglycan side chains.

Effects of low-molecular-weight dermatan sulfate on coagulation, fibrinolysis and tissue factor pathway inhibitor in healthy volunteers.

Low-molecular-weight (LMW)-dermatan sulfate (Desmin) with the mean molecular weight of 5600 Da has been obtained by limited depolymerization of natural dermatan sulfate. The pharmacokinetic and pharmacodynamic data of 100 and 200 mg were analyzed after intravenous injection and of 50, 100 and 200 mg after subcutaneous injection on tissue factor pathway inhibitor (TFPI) antigen and activity, heparin cofactor (HC) II activity, HeptestTM coagulation value, chromogenic S-2222 anti-factor Xa (aXa) assay, activated partial thromboplastin time (APTT), thrombin clotting time (TCT), plasminogen, tissue plasminogen activator activity (t-PA) and plasminogen activator inhibitor (PAI). After i.v.injection of 100 mg and 200 mg Desmin TFPI antigen and activity increased 2.2- and 2.7-fold, and returned to normal values within 60 and 90 min, respectively. Using the HC II assay the elimination half-lives (T1/2 el) increased from 1.9 h to 3.3 h with increasing doses of LMW-dermatan sulfate. T1/2 el were 4.3 and 6.9 h with the Heptest assay and 3.3 and 5.1 with the aXa method, respectively. APTT, TCT and the fibrinolytic parameters were not modified by either dose of i.v. LMW-dermatan sulfate. After s.c. administration of 100 mg or 200 mg LMW-dermatan sulfate no increase of TFPI antigen or activity was detected. T1/2 el was 5.6 h using HC II method, 11.1 h using Heptest and 7.8 h with the aXa activity. The total clearance was about ten-fold higher when determined by the HC II method compared with Heptest and aXa method. The volume of distribution (VD) increased with increasing doses of s.c. LMW-dermatan sulfate and was highest with the HC II method. Intravenous administration of 100 mg protamine chloride 15 min after i.v. dosing of 100 mg LMW-dermatan sulfate did not modify TFPI, coagulation or fibrinolytic parameters. Further analysis of the complex mechanism of action has to include studies which should explain the low release of TFPI in relation to the antithrombotic effects of LMW-dermatan sulfate.

Depolymerization of coal by phenolation: a review

The literature on the acidic depolymerization of coal in phenol is reviewed. The reaction is believed to be an interesting technique for studies of the organic chemical structure of coal, as it renders more than 90 wt% of coal extractable in pyridine and produces low molecular weight (MW) products. However, recent studies have shown that this reaction leads to polymeric products with only limited depolymerization of the coal. Pyridine extracts of depolymerized coal are contaminated with 10–40 wt% of colloidal suspensions and research is needed to bring about efficient depolymerization, to facilitate structural studies on coal.

The effect of cross-linking spectrin-actin complexes with band 4.1 on the state of polymerization of the actin

The polymerization of actin in the presence of spectrin tetramers and band 4.1 isolated from the human erythrocyte has been measured using a fluorescence energy transfer technique. The results show that the cross-linking of spectrin-actin complexes by band 4.1 results in a limited depolymerization of actin filaments and a concomitant rise in the critical actin concentration. The phenomenon may explain in part the existence of actin in the erythrocyte cytoskeleton as short oligomers rather than as long filaments.

Equilibrium and kinetic analysis of microtubule assembly in the presence of guanosine diphosphate

In this paper we expand upon a previously reported observation of the effects of GDP on microtubule assembly. A ratio of GDP to GTP of ten (1 m m-GDP and 0.1 m m-GTP) is generally sufficient to completely block microtubule assembly, but only limited depolymerization is induced if GDP is added after assembly has reached a plateau in the presence of GTP. When added during polymerization, GDP arrests further elongation, and greater steady-state levels of assembly are obtained the later the time of addition of GDP. To explain this behavior we examined the rates of assembly and disassembly and the apparent critical concentration ( C 0) of tubulin in the presence of GDP. GDP-tubulin polymerizes very slowly as compared to GTP-tubulin, while depolymerization rates, as determined by dilution, are nearly identical in GTP and GDP. The C 0 value calculated from the assembly and disassembly rates in GTP is within experimental error of the C 0 value at steady-state determined directly. In the presence of GDP, however, the C 0 value calculated from rate measurements is at least 60 times greater than that determined by equilibrium analysis. Our results indicate that the net assembly rate in GDP is not a valid measure of the reaction occurring at steady-state. A limited amount of depolymerization may occur upon addition of GDP to microtubules, and this appears to be due to a decrease in the fraction of protein able to participate in the polymerization reaction. The amount of tubulin “inactivated” by GDP is increased by the removal of microtubule-associated proteins. GDP-tubulin will stabilize existing microtubules, even when its polymerization cannot be demonstrated. These results are inconsistent with present models of microtubule assembly, and a new model involving co-operative interaction of microtubule-associated protein-tubulin oligomers at microtubule ends is proposed.

The bilirubin-induced photodegradation of deoxyribonucleic acid.

The widespread use of phototherapy for neonatal jaundice has caused some concern since little is known about the cellular consequences of such treatment. The present study was undertaken to determine the effects of photoactivated bilirubin on the structure of purified deoxyribonucleic acid. DNA illuminated in the presence of bilirubin exhibited altered physical chemical properties as evidence by (1) a changed thermal helix coil transition profile, (2) a sensitivity of the treated DNA to alkaline degradation, and (3) a limited depolymerization of single-stranded DNA. The above changes were observed with a total light dosage representing only 5% of that received by a newborn infant during a 24-hr period of phototherapy in our nursery. In view of the known relationship between ability to modify cellular DNA and mutagenic and/or carcinogenic potential, the present results suggest that phototherapy is a complex process which may have potentially dangerous sequelae.