Editing Isoprene (section)

==Natural occurrences==
[[Image:Dimethylallyl diphosphate.svg|thumb|[[Dimethylallyl pyrophosphate]], not isoprene itself, is the source of most terpenes.|left]]
Isoprene is produced and emitted by many species of trees (major producers are [[oak]]s, [[poplars]], [[eucalyptus]], and some legumes). Yearly production of isoprene emissions by vegetation is around 600 million [[metric ton]]s, half from tropical broadleaf trees and the remainder primarily from [[shrub]]s.<ref>{{cite journal | vauthors = Guenther A, Karl T, Harley P, Wiedinmyer C, Palmer PI, Geron C  |title=Estimates of global terrestrial isoprene emissions using MEGAN (Model of Emissions of Gases and Aerosols from Nature) |journal=Atmospheric Chemistry and Physics |volume=6 |issue=11 |pages=3181–3210 |year=2006 |doi=10.5194/acp-6-3181-2006 |bibcode=2006ACP.....6.3181G |doi-access=free |hdl=20.500.11820/429435d3-e131-45e2-8bba-42a3d552cc59 |hdl-access=free }}</ref> This is about equivalent to [[methane emissions]] and accounts for around one-third of all [[hydrocarbons]] released into the atmosphere. In [[deciduous]] forests, isoprene makes up approximately 80% of hydrocarbon emissions. While their contribution is small compared to trees, microscopic and macroscopic [[algae]] also produce isoprene.<ref>{{cite journal | vauthors = Johnston A, Crombie AT, El Khawand M, Sims L, Whited GM, McGenity TJ, Colin Murrell J | title = Identification and characterisation of isoprene-degrading bacteria in an estuarine environment | journal = Environmental Microbiology | volume = 19 | issue = 9 | pages = 3526–3537 | date = September 2017 | pmid = 28654185 | pmc = 6849523 | doi = 10.1111/1462-2920.13842 }}</ref>

===Plants===
Isoprene is made through the [[Non-mevalonate pathway|methyl-erythritol 4-phosphate pathway]] (MEP pathway, also called the non-[[mevalonate pathway]]) in the [[chloroplast]]s of plants. One of the two end-products of MEP pathway, [[dimethylallyl pyrophosphate]] (DMAPP), is cleaved by the enzyme [[isoprene synthase]] to form isoprene and diphosphate. Therefore, inhibitors that block the MEP pathway, such as [[fosmidomycin]], also block isoprene formation. Isoprene emission increases dramatically with temperature and maximizes at around 40&nbsp;°C. This has led to the hypothesis that isoprene may protect plants against heat stress (thermotolerance hypothesis, see below). Emission of isoprene is also observed in some bacteria and this is thought to come from non-enzymatic degradations from DMAPP. Global emission of isoprene by plants is estimated at 350 million tons per year.<ref>{{Cite web |last= |first= |title=Isoprene emissions version 2021 |url=https://emissions.aeronomie.be/index.php/bottom-up/isoprenev2021 |access-date=2022-09-26 |website=emissions.aeronomie.be |language=en}}</ref>

====Regulation====
Isoprene emission in plants is controlled both by the availability of the substrate (DMAPP) and by [[enzyme]] (isoprene synthase) activity. In particular, light, CO<sub>2</sub> and O<sub>2</sub> dependencies of isoprene emission are controlled by substrate availability, whereas temperature dependency of isoprene emission is regulated both by substrate level and enzyme activity.

=== Human & other organisms ===
Isoprene is the most abundant hydrocarbon measurable in the breath of humans.<ref name="Gelmont">{{cite journal | vauthors = Gelmont D, Stein RA, Mead JF | title = Isoprene-the main hydrocarbon in human breath | journal = Biochemical and Biophysical Research Communications | volume = 99 | issue = 4 | pages = 1456–60 | date = April 1981 | pmid = 7259787 | doi = 10.1016/0006-291X(81)90782-8 }}</ref><ref name="King">{{cite journal | vauthors = King J, Koc H, Unterkofler K, Mochalski P, Kupferthaler A, Teschl G, Teschl S, Hinterhuber H, Amann A | display-authors = 6 | title = Physiological modeling of isoprene dynamics in exhaled breath | journal = Journal of Theoretical Biology | volume = 267 | issue = 4 | pages = 626–37 | date = December 2010 | pmid = 20869370 | doi = 10.1016/j.jtbi.2010.09.028 | arxiv = 1010.2145 | bibcode = 2010JThBi.267..626K | s2cid = 10267120 | author7-link = Susanne Teschl }}</ref><ref>{{cite journal | vauthors = Williams J, Stönner C, Wicker J, Krauter N, Derstroff B, Bourtsoukidis E, Klüpfel T, Kramer S | display-authors = 6 | title = Cinema audiences reproducibly vary the chemical composition of air during films, by broadcasting scene specific emissions on breath | journal = Scientific Reports | volume = 6 | pages = 25464 | date = May 2016 | pmid = 27160439 | doi = 10.1038/srep25464 | pmc = 4862009 | bibcode = 2016NatSR...625464W }}</ref> The estimated production rate of isoprene in the human body is 0.15 [[mole (unit)|μmol]]/(kg·h), equivalent to approximately 17&nbsp;mg/day for a person weighing 70&nbsp;kg. Human breath isoprene originates from lipolytic cholesterol metabolism within the skeletal muscular peroxisomes and ''IDI2'' gene acts as the production determinant.<ref>{{Cite journal |last=Sukul |first=Pritam |last2=Richter |first2=Anna |last3=Junghanss |first3=Christian |last4=Schubert |first4=Jochen K. |last5=Miekisch |first5=Wolfram |date=2023-09-30 |title=Origin of breath isoprene in humans is revealed via multi-omic investigations |url=https://www.nature.com/articles/s42003-023-05384-y |journal=Communications Biology |language=en |volume=6 |issue=1 |pages=1–12 |doi=10.1038/s42003-023-05384-y |issn=2399-3642|pmc=10542801 }}</ref> Due to the absence of ''IDI2'' gene, animals such as pigs and bottle-nose dolphins do not exhale isoprene.

Isoprene is common in low concentrations in many foods. Many species of soil and marine bacteria, such as [[Actinomycetota]], are capable of degrading isoprene and using it as a fuel source. 
[[File:PolyIsopreneCorrected.svg|thumb|350px|left|Chemical structure of ''cis''-polyisoprene, the main constituent of natural rubber]]