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Rubber, natural biosynthesis

Natural Rubber Biosynthesis, Structure, Properties and Application... [Pg.48]

Puskas, J. E., Gautriaud, E., Deffieux, A., Kennedy, J. P. Natural rubber biosynthesis—a living carbocationic polymerization frog. Polym. Sci. 2006, 31(6), 533-548. [Pg.33]

The biosynthesis of synthetic natural rubber has been completely determined and appears in Fig. 15.1. Many plants and animals use this same biosynthetic pathway to make hundreds of terpenes and steroids from their common isoprenoid building blocks. [Pg.278]

Rubber is synthesized by plants via a side branch of the isoprenoid pathway by the enzyme rubber transferase (dy-prenyl transferase systematic name poly-dy-polyprenyl-diphosphate isopentenyl-diphosphate polyprenylcistransferase EC 2.5.1.20). Surprisingly, although this process has been studied for decades, due to the labile nature of the rubber transferase and the fact that it is a membrane-associated enzyme present in relatively low abundance, the identification of its protein subunits remain elusive. For some recent reviews on rubber biosynthesis, please refer to [248-251]. [Pg.43]

All rubber transferases exhibit similar kinetic constants and pH optima, and are able to accept a similar range of APPs as initiating substrate [263, 264], In vitro studies have shown that several compounds (DMAPP, GPP, FPP, and GGPP) can initiate rubber biosynthesis, with a faster rate of rubber biosynthesis the longer the APP (up to C15 or C20) [254, 265], Non-natural APPs were also shown to be able to function as a primer for the rubber biosynthesis [266],... [Pg.45]

The cDNAs of the cA-prenyltransferase of H. brasiliensis was successfully identified and expressed in E. coli. The in vitro polymerization of IPP after initiation with FPP using the expressed c/x-prenyltransferase resulted in low degrees of polymerization [267, 268]. After addition of rubber particles to this polymerization, the molecular weight increased tremendously [269], It can be concluded that the rubber particles are essential for rubber biosynthesis. Katarina Cornish established a detailed structural model of the in vivo synthesis of natural rubber in the rubber particle monolayer membrane and partially explained this behavior (see Fig. 12) [251],... [Pg.45]

In addition to its role as an intermediate in cholesterol biosynthesis, isopentenyl pyrophosphate is the activated precursor of a huge array of biomolecules with diverse biological roles (Fig. 21-48). They include vitamins A, E, and K plant pigments such as carotene and the phytol chain of chlorophyll natural rubber many essential oils (such as the fragrant principles of lemon oil, eucalyptus, and musk) insect juvenile hormone, which controls metamorphosis dolichols, which serve as lipid-soluble carriers in complex polysaccharide synthesis and ubiquinone and plastoquinone, electron carriers in mitochondria and chloroplasts. Collectively, these molecules are called isoprenoids. More than... [Pg.828]

The biosynthesis of natural rubber has been studied from the viewpoint of an elucidation of initiation and propagation mechanisms mainly by tracer techniques. The steps in the formation of isopentenyl pyrophosphate from acetyl-coA via mevalonate are now well established in the in vitro synthesis of rubber. It has also been confirmed that chain extension occurs on the surface of existing rubber particles by successive additions of isopentenyl pyrophosphate to build up chains of 5000-7000 isoprene units (4,5). The initiation step of rubber formation, however, remains unknown due to the lack of detailed information concerning the direct precursor of the chain extension. [Pg.234]

Polymers are classified as either natural that resulted from natural biosynthesis, or synthetic. The natural (polysaccharides, proteins, nucleic acids, natural rubbers, cellulose, lignin, etc.) have been used for tens of thousands of years. In Egypt the musical string instruments, papyrus for writing, and styrene [in a tree balsam] for embalming were used 3,000 BC. For millennia shellac has been used in Indian turnery [Chattopadhyaya, 1986]. The natural rubber was used by Olmecs at least 3000 years ago [Stuart, 1993]. [Pg.1]

In this section the biosynthesis of bacterial polyhydroxyallcanoates, natural rubber and cellulose is discussed, whilst simultaneously describing analogies with synthetic emulsion polymerization processes. [Pg.398]

Natural rubber is synthesized by a wide variety of plants. The botanic rationale for this synthesis is still a mystery. The biosynthesis of natural rubber has been studied extensively in the past [47-50], and the basic polymerization reactions have been defined. However, the full mechanism of formation of the rubber particles has still not been elucidated, although some suggestions have been made [48,50,51],... [Pg.805]

Poly(cii-l,4-isoprene) is the polymer that gives natural rubber a very competitive share of the elastomer market. In Hevea brasiliensis latex, this polymer is stored in so-called rubber particles , which make up 20 to 45% of the latex volume. Much work has been undertaken to understand the biosynthesis pathway of this very-long-chain polymer, which stands out through having almost 100% cis double bonds. [Pg.347]

Chromenes, Benzofurans, Benzopyrans, and Precocenes Polyterpenes Biosynthesis Biological Activity Natural Rubber Hevea brasiliensis Guayule Gutta Percha Chicle... [Pg.312]

The biosynthesis of rubber may be divided into three steps (1) initiation, which requires an allylic diphosphate molecule, (2) elongation, in which IPP units are added to a Z-l,4-polyisoprene chain, and (3) termination, in which the polymer is released from the rubber transferase enzyme (Cornish, 1993). In plants, the elongation of Z-l,4-polyiso-prene (natural rubber) requires a small -allylic diphosphate initiator (less than or equal to C20). Famesyl pyrophosphate (FPP) is an effective initiator of polyisoprene biosynthesis (Light et al, 1989) further, because only one molecule of FPP is needed for each molecule of rubber formed, small traces of this substance that are inadvertently present complicate biosynthetic studies. The E-allylic diphosphates are hydrophilic cytosolic compounds, whereas Z-l,4-polyisoprene is hydrophobic and compartmentalized in subcellular rubber particles. A soluble E-prenyl transferase from the latex of Hevea brasiliensis serves as a famesyl diphosphate synthase and plays no direct role in elongation of Z-l,4-polyisoprene (Cornish, 1993). Because the hydro-phobic rubber molecule is produced inside a rubber particle but is formed from hydrophilic precursors from the cytoplasm, the polymerization reaction must take place at the particle surface. [Pg.319]


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See also in sourсe #XX -- [ Pg.412 ]

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See also in sourсe #XX -- [ Pg.234 , Pg.244 ]




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