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Katrina Cornish - One of the best experts on this subject based on the ideXlab platform.
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Protein farnesyltransferase inhibitors interfere with farnesyl diphosphate binding by Rubber transferase.
European journal of biochemistry, 2003Co-Authors: Christopher J. D. Mau, John C. Vederas, Sylvie Garneau, Andrew Scholte, Jennifer E. Van Fleet, Katrina CornishAbstract:Rubber transferase, a cis-prenyltransferase, catalyzes the addition of thousands of isopentenyl diphosphate (IPP) Molecules to an allylic diphosphate initiator, such as farnesyl diphosphate (FPP, 1), in the presence of a divalent metal cofactor. In an effort to characterize the catalytic site of Rubber transferase, the effects of two types of protein farnesyltransferase inhibitors, several chaetomellic acid A analogs (2, 4–7) and α-hydroxyfarnesylphosphonic acid (3), on the ability of Rubber transferase to add IPP to the allylic diphosphate initiator were determined. Both types of compounds inhibited the activity of Rubber transferases from Hevea brasiliensis and Parthenium argentatum, but there were species–specific differences in the inhibition of Rubber transferases by these compounds. Several shorter analogs of chaetomellic acid A did not inhibit Rubber transferase activity, even though the analogs contained chemical features that are present in an elongating Rubber Molecule. These results indicate that the initiator-binding site in Rubber transferase shares similar features to FPP binding sites in other enzymes.
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Regulation of initiation and polymer molecular weightof cis-1,4-polyisoprene synthesized in vitro by particlesisolated from Parthenium argentatum (Gray)
Phytochemistry, 1999Co-Authors: Javier Castillón, Katrina CornishAbstract:Parthenium argentatum is a prime candidate for development as a new crop for theproduction of natural Rubber (cis-1,4-polyisoprene). The Rubber obtained from P. argentatum iscomparable in molecular weight (and quality) to that obtained from Hevea brasiliensis (Mr ca.106 Da), which is currently the sole commercial source of natural Rubber. Most of the 2500Rubber-producing plant species known make much lower molecular weight Rubber, although theregulation of polymer molecular weight is not understood. In the experiments reported here,we investigated the regulation of Rubber biosynthesis and polymer molecular weight usingpurified, enzymatically-active Rubber particles isolated from P. argentatum, under variousconcentrations of the allylic diphosphate (allylic-PP) Rubber Molecule initiators farnesyldiphosphate (FPP, a 15-carbon Molecule), or geranyl diphosphate (GPP, a 10-carbon Molecule)and the elongation substrate isopentenyl diphosphate (IPP). Our results show that the rates ofboth Rubber Molecule initiation and polymerization, and the final polymer molecular weight,were greatly affected by the concentration of initiator and IPP. Increasing allylic-PP initiatorconcentrations caused an increase in the amount of Rubber synthesized and the number ofMolecules initiated but a decrease in the mean polymer molecular weight; increasing IPPconcentrations increased the amount of Rubber and the mean polymer molecular weight. Atidentical substrate concentrations of IPP and allylic-PP, GPP initiated about one third of theRubber polymers initiated by FPP but incorporated about two thirds the amount of IPP, comparedto FPP. Consequently, while the amount of Rubber synthesized in the presence of GPP was lessthan with FPP, the Rubber polymers synthesized with GPP initiator were, on average, about twicethe molecular weight of those with FPP.
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Effect of Different Allylic Diphosphates on the Initiation of New Rubber Molecules and on Cis-1,4-polyisoprene Biosynthesis in Guayule (Parthenium argentatum Gray)
Journal of Plant Physiology, 1995Co-Authors: Katrina Cornish, Deborah J. SilerAbstract:Summary Natural Rubber biosynthesis is the Rubber-particle-bound Rubber-transferase-catalyzed cis-1,4-polymerization of isoprene monomers derived from isopentenyl diphosphate (IPP). In addition to IPP, allylic diphosphate is required to initiate new Rubber Molecules. In this paper we describe, for the first time, detailed kinetic analyses of Rubber Molecule initiation and polymerization in Parthenium argentatum Gray . We compare the effects of four different allylic diphosphate initiators on the rate of Rubber biosynthesis using [ 14 C]IPP. Also, we compare the rates of Rubber Molecule initiation and polymerization using [ 3 H]allylic diphosphates as well as [ 14 C]IPP. Under non-limiting substrate concentrations, new Rubber Molecules were initiated and terminated at a constant rate for each initiator. The rate of Rubber biosynthesis increased with the chain length of the initiator up to C,s. Our results indicate that initiation regulates the overall rate of Rubber biosynthesis. Therefore, strategies to enhance in vivo Rubber yield by genetic manipulation should focus on Rubber Molecule initiation.
David E Hanson - One of the best experts on this subject based on the ideXlab platform.
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how far can a Rubber Molecule stretch before breaking ab initio study of tensile elasticity and failure in single Molecule polyisoprene and polybutadiene
Journal of Chemical Physics, 2009Co-Authors: David E Hanson, Richard L MartinAbstract:We present ab initio calculations of the internal C–C bond dissociation curve for single Molecules of (cis-1,4) polyisoprene and polybutadiene. We define “bond rupture” as that point on the reaction coordinate where the unrestricted Kohn–Sham, or diradical, solution falls below the restricted, or closed-shell, solution. Using this definition, we find that rupture occurs at a tensile force of 6.8 nN for polyisoprene and 7.2 nN for polybutadiene. Their respective rupture strains are 45% and 42%. Our calculations show that the energy density versus extension is not sensitive to the number of isoprene units contained in the Molecule, i.e., it is essentially independent of the chain length. These relatively large rupture strains have important implications for understanding the failure mechanism in Rubber, and imply that purely enthalpic chain stretching must commence well before tensile failure occurs.
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how far can a Rubber Molecule stretch before breaking ab initio study of tensile elasticity and failure in single Molecule polyisoprene
Polymer, 2008Co-Authors: David E HansonAbstract:We present ab initio calculations of the internal C-C bond dissociation curve for single Molecules of (cis 1,4) polyisoprene, polybutadiene, and polyethylene, all of comparable length. We define 'bond rupture' as that point on the reaction coordinate where the unrestricted Kohn-Sham, or diradical, solution falls below the restricted, or closed-shell, solution. Using this well-defined though crude approximation, we find that rupture occurs at a tensile force of 6.8 nN for poly isoprene and 7.2 nN for polybutadiene. Their respective rupture strains are 45% and 42%. Our calculations show that the energy density vs. extension is not sensitive to the length of the Molecule, i.e., it is essentially independent of the number of isoprene units contained. These relatively large rupture strains have important implications for understanding the failure mechanism in Rubber, and imply that purely enthalpic chain stretching must commence well before tensile failure occurs.
Richard L Martin - One of the best experts on this subject based on the ideXlab platform.
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how far can a Rubber Molecule stretch before breaking ab initio study of tensile elasticity and failure in single Molecule polyisoprene and polybutadiene
Journal of Chemical Physics, 2009Co-Authors: David E Hanson, Richard L MartinAbstract:We present ab initio calculations of the internal C–C bond dissociation curve for single Molecules of (cis-1,4) polyisoprene and polybutadiene. We define “bond rupture” as that point on the reaction coordinate where the unrestricted Kohn–Sham, or diradical, solution falls below the restricted, or closed-shell, solution. Using this definition, we find that rupture occurs at a tensile force of 6.8 nN for polyisoprene and 7.2 nN for polybutadiene. Their respective rupture strains are 45% and 42%. Our calculations show that the energy density versus extension is not sensitive to the number of isoprene units contained in the Molecule, i.e., it is essentially independent of the chain length. These relatively large rupture strains have important implications for understanding the failure mechanism in Rubber, and imply that purely enthalpic chain stretching must commence well before tensile failure occurs.
Yasuyuki Tanaka - One of the best experts on this subject based on the ideXlab platform.
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Structural characterization of alpha-terminal group of natural Rubber. 1. Decomposition of branch-points by lipase and phosphatase treatments.
Biomacromolecules, 2005Co-Authors: Lucksanaporn Tarachiwin, Jitladda Sakdapipanich, Koichi Ute, Tatsuki Kitayama, Takashi Bamba, Eiichiro Fukusaki, And Akio Kobayashi, Yasuyuki TanakaAbstract:Deproteinized natural Rubber latex (DPNR-latex) was treated with lipase and phosphatase in order to analyze the structure of the chain-end group (alpha-terminal). The enzymatic treatment decreased the content of long-chain fatty acid ester groups in DPNR from about 6 to 2 mol per Rubber Molecule. The molecular weight and intrinsic viscosity were reduced to about one-third after treatment with lipase and phosphatase. The Huggins' k' constant of the enzyme-treated DPNR showed the formation of linear Rubber Molecules. The molecular weight distribution of DPNR changed apparently after treatment with lipase and phosphatase. (1)H NMR spectrum of Rubber obtained from DPNR-latex showed small signals due to monophosphate, di-phosphate and phospholipids at the alpha-terminus. Treatment of DPNR-latex with lipase and phosphatase decreased the relative intensity of the (1)H NMR signals corresponding to phospholipids, whereas no change was observed for the signals due to mono- and diphosphates. The residual mono- and diphosphate signals as well as some phospholipid signals after lipase and phosphatase treatments indicate that mono- and diphosphate groups are directly linked at the alpha-terminus with the modified structure, expected by aggregation or linking with phospholipid Molecules.
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Effect of Gel on the Green Strength of Natural Rubber
Rubber Chemistry and Technology, 2002Co-Authors: Seiichi Kawahara, Jitladda Sakdapipanich, Yasuyuki Tanaka, Yoshinobu Isono, Eng Aik-hweeAbstract:Abstract The outstanding properties of natural Rubber, e.g., green strength and rapid crystallization, were attributed to the chemical branching that formed at both chain ends of the Rubber Molecule during the preservation of the latex in the presence of ammonia. The gel content of natural Rubbers from various clonal origins increased during the preservation, but decreased after deproteinization of the aged latex. The crystallization of acetone-extracted Rubber was slightly suppressed as the gel content increased. The increase in green strength during the preservation was studied in connection with the gel content and degree of branching of the Rubber.
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Crystallization behavior and strength of natural Rubber: Skim Rubber, deproteinized natural Rubber, and pale crepe
Journal of Applied Polymer Science, 2000Co-Authors: Seiichi Kawahara, Takashi Kakubo, Naoyuki Nishiyama, Yasuyuki Tanaka, Yoshinobu Isono, Jitladda SakdapipanichAbstract:Crystallization behavior of natural Rubber prepared by different procedures, such as skim Rubber, deproteinized natural Rubber (DPNR), and pale crepe, was investigated by dilatometry at −25°C. DPNR was fractionated into four fractions by molecular weight. The high molecular weight fractions contained about 1.7 linked fatty acids per Rubber Molecule, while low molecular weight fraction showed an increase in quantity. The overall crystallization rate of the Rubber decreased as the molecular weight decreased. Skim Rubbers, purified by extraction with acetone, crystallized rapidly compared to acetone-extracted pale crepe, despite that the molecular weight of skim Rubbers was about one-half of pale crepe. The quantity of linked fatty acid per Rubber Molecule of skim Rubbers was less than 0.5, while that of pale crepe was 1.6. The difference in the rate of crystallization was presumed to be associated with the level of fatty acids linked to Rubber Molecule at the terminal and branch points present in pale crepe. The green strength of skim Rubbers was significantly lower than those of untreated pale crepe and DPNR, but was comparable to transesterified DPNR, which contains no gel fraction and no linked fatty acids. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1510–1516, 2000
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Origin of Characteristic Properties of Natural Rubber—Synergistic Effect of Fatty Acids on Crystallization of cis-1,4-Polyisoprene: II, Mixed and Esterified Fatty Acids in Natural Rubber
Rubber Chemistry and Technology, 1996Co-Authors: Naoyuki Nishiyama, Seiichi Kawahara, Takashi Kakubo, Eng Aik Hwee, Yasuyuki TanakaAbstract:Abstract Crystallization behavior of deproteinized natural Rubber at −25°C was investigated by dilatometry in connection with the effect of long-chain fatty acid groups, esterified to the Rubber chain, as well as free fatty acids and their esters. The overall crystallization rate decreased after removal of the acetone-extractable free fatty acids and their esters, while it increased significantly when the fatty acid groups esterified to natural Rubber Molecule were removed by transesterification with sodium methoxide. Both the acetone-extracted and transesterified Rubbers showed a significant increase in the overall crystallization rate after the addition of 1 wt % stearic acid. The crystallization of acetone-extracted Rubber was accelerated by the addition of 1 wt % methyl linoleate, a plasticizer of natural Rubber, whereas it was suppressed in the case of transesterified Rubber in which the esterified fatty acid groups were removed completely. The fatty acid groups esterified to natural Rubber Molecule ...
Jitladda Sakdapipanich - One of the best experts on this subject based on the ideXlab platform.
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Investigating the Mechanistic and Structural Role of Lipid Hydrolysis in the Stabilization of Ammonia-Preserved Hevea Rubber Latex
2018Co-Authors: Sirirat Kumarn, Nut Churinthorn, Adun Nimpaiboon, Manus Sriring, Atsushi Takahara, Jitladda SakdapipanichAbstract:The stabilization mechanism of natural Rubber (NR) latex from Hevea brasiliensis was studied to investigate the components involved in base-catalyzed ester hydrolysis, namely, hydrolyzable lipids, ammonia, and the products responsible for the desired phenomenon observed in ammonia-preserved NR latex. Latex stability is generally thought to come from a Rubber particle (RP) dispersion in the serum, which is encouraged by negatively charged species distributed on the RP surface. The mechanical stability time (MST) and zeta potential were measured to monitor field latices preserved in high (FNR-HA) and low ammonia (FNR-LA) contents as well as that with the ester-containing components removed (saponified NR) at different storage times. Amounts of carboxylates of free fatty acids (FFAs), which were released by the transformation and also hypothesized to be responsible for the like-charge repulsion of RPs, were measured as the higher fatty acid (HFA) number and corroborated by confocal laser scanning microscopy (CLSM) both qualitatively and quantitatively. The lipids and their FFA products interact differently with Nile red, which is a lipid-selective and polarity-sensitive fluorophore, and consequently re-emit characteristically. The results were confirmed by conventional ester content determination utilizing different solvent extraction systems to reveal that the lipids hydrolyzed to provide negatively charged fatty acid species were mainly the polar lipids (glycolipids and phospholipids) at the RP membrane but not those directly linked to the Rubber Molecule and, to a certain extent, those suspended in the serum. From new findings disclosed herein together with those already reported, a new model for the Hevea Rubber particle in the latex form is proposed
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CHAPTER 2:Natural Rubber: Biosynthesis, Structure, Properties and Application
Polymer Chemistry Series, 2013Co-Authors: Jitladda Sakdapipanich, Porntip RojruthaiAbstract:Rubber from Hevea brasiliensis, known as natural Rubber (NR), contains Rubber hydrocarbon and ca. 6% of non-Rubber components. The biosynthesis of the NR latex particles takes place in the laticifers of the Hevea Rubber tree. Rubber Molecule is synthesized by the addition of isopentenyl diphosphate into farnesyl diphosphate, the initiating Molecule, catalysed by Rubber transferases (EC 5.3.3.2). The Rubber Molecule is known to be composed of a long polymer chain with branched points. The fundamental chain was found to be consisting of a long sequence of cis-1,4-isoprene units having two trans-1,4-isoprene units at the initiating terminal. Both initiating- and terminating-terminal of Rubber Molecules and the branching formation will be discussed in detail.
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Structural characterization of alpha-terminal group of natural Rubber. 1. Decomposition of branch-points by lipase and phosphatase treatments.
Biomacromolecules, 2005Co-Authors: Lucksanaporn Tarachiwin, Jitladda Sakdapipanich, Koichi Ute, Tatsuki Kitayama, Takashi Bamba, Eiichiro Fukusaki, And Akio Kobayashi, Yasuyuki TanakaAbstract:Deproteinized natural Rubber latex (DPNR-latex) was treated with lipase and phosphatase in order to analyze the structure of the chain-end group (alpha-terminal). The enzymatic treatment decreased the content of long-chain fatty acid ester groups in DPNR from about 6 to 2 mol per Rubber Molecule. The molecular weight and intrinsic viscosity were reduced to about one-third after treatment with lipase and phosphatase. The Huggins' k' constant of the enzyme-treated DPNR showed the formation of linear Rubber Molecules. The molecular weight distribution of DPNR changed apparently after treatment with lipase and phosphatase. (1)H NMR spectrum of Rubber obtained from DPNR-latex showed small signals due to monophosphate, di-phosphate and phospholipids at the alpha-terminus. Treatment of DPNR-latex with lipase and phosphatase decreased the relative intensity of the (1)H NMR signals corresponding to phospholipids, whereas no change was observed for the signals due to mono- and diphosphates. The residual mono- and diphosphate signals as well as some phospholipid signals after lipase and phosphatase treatments indicate that mono- and diphosphate groups are directly linked at the alpha-terminus with the modified structure, expected by aggregation or linking with phospholipid Molecules.
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Effect of Gel on the Green Strength of Natural Rubber
Rubber Chemistry and Technology, 2002Co-Authors: Seiichi Kawahara, Jitladda Sakdapipanich, Yasuyuki Tanaka, Yoshinobu Isono, Eng Aik-hweeAbstract:Abstract The outstanding properties of natural Rubber, e.g., green strength and rapid crystallization, were attributed to the chemical branching that formed at both chain ends of the Rubber Molecule during the preservation of the latex in the presence of ammonia. The gel content of natural Rubbers from various clonal origins increased during the preservation, but decreased after deproteinization of the aged latex. The crystallization of acetone-extracted Rubber was slightly suppressed as the gel content increased. The increase in green strength during the preservation was studied in connection with the gel content and degree of branching of the Rubber.
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Crystallization behavior and strength of natural Rubber: Skim Rubber, deproteinized natural Rubber, and pale crepe
Journal of Applied Polymer Science, 2000Co-Authors: Seiichi Kawahara, Takashi Kakubo, Naoyuki Nishiyama, Yasuyuki Tanaka, Yoshinobu Isono, Jitladda SakdapipanichAbstract:Crystallization behavior of natural Rubber prepared by different procedures, such as skim Rubber, deproteinized natural Rubber (DPNR), and pale crepe, was investigated by dilatometry at −25°C. DPNR was fractionated into four fractions by molecular weight. The high molecular weight fractions contained about 1.7 linked fatty acids per Rubber Molecule, while low molecular weight fraction showed an increase in quantity. The overall crystallization rate of the Rubber decreased as the molecular weight decreased. Skim Rubbers, purified by extraction with acetone, crystallized rapidly compared to acetone-extracted pale crepe, despite that the molecular weight of skim Rubbers was about one-half of pale crepe. The quantity of linked fatty acid per Rubber Molecule of skim Rubbers was less than 0.5, while that of pale crepe was 1.6. The difference in the rate of crystallization was presumed to be associated with the level of fatty acids linked to Rubber Molecule at the terminal and branch points present in pale crepe. The green strength of skim Rubbers was significantly lower than those of untreated pale crepe and DPNR, but was comparable to transesterified DPNR, which contains no gel fraction and no linked fatty acids. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1510–1516, 2000
