Editing Natural rubber (section)

===Biosynthesis===
Rubber particles are formed in the [[cytoplasm]] of specialized latex-producing cells called [[laticifer]]s within rubber plants.<ref>{{cite book |editor-last=Koyama |editor-first=Tanetoshi |editor2-last=Steinbüchel |editor2-first=Alexander |chapter=Biosynthesis of Natural Rubber and Other Natural Polyisoprenoids |title=Polyisoprenoids |chapter-url={{google books |plainurl=y |id=1a_wAAAAMAAJ |page=73}} |series=Biopolymers |volume=2 |publisher=Wiley-Blackwell |date=June 2011 |pages=73–81 |isbn=978-3-527-30221-5}}</ref> Rubber particles are surrounded by a single [[phospholipid]] membrane with [[hydrophobic]] tails pointed inward. The membrane allows biosynthetic proteins to be sequestered at the surface of the growing rubber particle, which allows new monomeric units to be added from outside the biomembrane, but within the lacticifer. The rubber particle is an enzymatically active entity that contains three layers of material, the rubber particle, a biomembrane and free monomeric units. The biomembrane is held tightly to the rubber core by the high negative charge along the double bonds of the rubber polymer backbone.<ref>{{cite journal |last1=Paterson-Jones |first1=J.C. |last2=Gilliland |first2=M.G. |last3=Van Staden |first3=J. |title=The Biosynthesis of Natural Rubber |journal=Journal of Plant Physiology |volume=136 |issue=3 |pages=257–263 |date=June 1990 |doi=10.1016/S0176-1617(11)80047-7 |bibcode=1990JPPhy.136..257P |issn=0176-1617}}</ref> Free monomeric units and conjugated proteins make up the outer layer. The rubber precursor is [[isopentenyl pyrophosphate]] (an [[allyl group|allylic]] compound), which elongates by Mg<sup>2+</sup>-dependent condensation by the action of rubber transferase. The monomer adds to the pyrophosphate end of the growing polymer. {{citation needed|date=December 2019|reason=Citation removed as it was attributed to a predatory publisher.}} The process displaces the terminal high-energy pyrophosphate. The reaction produces a cis polymer. The initiation step is catalyzed by [[prenyltransferase]], which converts three monomers of isopentenyl pyrophosphate into [[farnesyl pyrophosphate]].<ref>{{cite journal |last1=Xie |first1=W. |display-authors=3 |last2=McMahan |first2=C.M. |last3=Distefano |first3=A.J. DeGraw, M.D. |last4=Cornish |first4=K. |last5=Whalen |first5=M. C. |last6=Shintani |first6=D.K. |date=2008 |title=Initiation of rubber synthesis: In vitro comparisons of benzophenone-modified diphosphate analogues in three rubber producing species |url=https://pubag.nal.usda.gov/pubag/downloadPDF.xhtml?id=22816&content=PDF |journal=Phytochemistry |volume=69 |issue=14 |pages=2539–2545 |doi=10.1016/j.phytochem.2008.07.011 |pmid=18799172 |bibcode=2008PChem..69.2539X |access-date=24 November 2019 |archive-date=2 October 2021 |archive-url=https://web.archive.org/web/20211002091715/https://pubag.nal.usda.gov/pubag/downloadPDF.xhtml?id=22816&content=PDF |url-status=dead }}</ref> The farnesyl pyrophosphate can bind to rubber transferase to elongate a new rubber polymer.

The required isopentenyl pyrophosphate is obtained from the [[mevalonate]] pathway, which derives from [[acetyl-CoA]] in the [[cytosol]]. In plants, isoprene pyrophosphate can also be obtained from the 1-deox-D-xyulose-5-phosphate/2-C-methyl-D-erythritol-4-phosphate pathway within plasmids.<ref>{{cite journal |last1=Casey |first1=P.J. |last2=Seabra |first2=M.C. |date=1996 |title=Protein Prenyltransferases |journal=Journal of Biological Chemistry |volume=271 |issue=10 |pages=5289–5292 |doi=10.1074/jbc.271.10.5289 |pmid=8621375 |doi-access=free}}</ref> The relative ratio of the farnesyl pyrophosphate initiator unit and isoprenyl pyrophosphate elongation monomer determines the rate of new particle synthesis versus elongation of existing particles. Though rubber is known to be produced by only one enzyme, extracts of latex host numerous small molecular weight proteins with unknown function. The proteins possibly serve as cofactors, as the synthetic rate decreases with complete removal.<ref>{{cite journal |last1=Kang |first1=H. |last2=Kang |first2=M.Y. |last3=Han |first3=K.H. |date=2000 |title=Identification of Natural Rubber and Characterization of Biosynthetic Activity |journal=Plant Physiol |volume=123 |issue=3 |pages=1133–1142 |doi=10.1104/pp.123.3.1133 |pmid=10889262 |pmc=59076}}</ref>