HMG-CoA reductase inhibitors, also known as the group of cholesterol-lowering drugs called statins, inhibit the synthesis of mevalonate. No adequate human studies of the relationship between isoprene exposure and human cancer have been reported.īiosynthesis and its inhibition by statins Tumors have been observed in multiple locations in multiple test species exposed to isoprene vapor. Addition of these chains to proteins is termed isoprenylation.Īccording to the United States Department of Health and Human Services Eleventh Edition Report on Carcinogens, isoprene is reasonably expected to be a human carcinogen. In virtually all organisms, isoprene derivatives are synthesized by the HMG-CoA reductase pathway. The functional isoprene units in biological systems are dimethylallyl pyrophosphate (DMAPP) and its isomer isopentenyl pyrophosphate (IPP), which are used in the biosynthesis of terpenes and lanosterol derivatives. Heme A has an isoprenoid tail, and lanosterol, the sterol precursor in animals, is derived from squalene and hence from isoprene. Also derived from isoprene are phytol, retinol ( vitamin A), tocopherol ( vitamin E), dolichols, and squalene. The terpenes (for example, the carotenes are tetraterpenes) are derived from isoprene, as are the terpenoids and coenzyme Q. It is a common structural motif in biological systems. Because of its atmospheric importance, much work has been devoted to emission studies from isoprene-emitting vegetation, and, kinetic and mechanistic studies of isoprene oxidation via OH radicals, ozone, and NO 3 radicals. Furthermore, isoprene forms secondary organic aerosols through photooxidation with OH radicals which also have wide-ranging health effects, particularly for the respiratory tract, and reduce visibility due to light scattering effects. Isoprene affects the oxidative state of large air masses, is an important precursor for ozone, a pollutant in the lower atmosphere. With a global biogenic production in the range of 400–600 Tg of carbon/year, isoprene has a large impact on atmospheric processes and is thus an important compound in the field of Atmospheric Chemistry. Thus, during the night, little isoprene is emitted from tree leaves while daytime emissions are expected to be substantial (~5-20 mg/m2/h) during hot and sunny days. The amount of isoprene released from isoprene-emitting vegetation depends on leaf mass, leaf area, light (particularly photosynthetic photon flux density), and leaf temperature. Isoprene is produced in the chloroplasts of leaves of certain tree species through the DMAPP pathway the enzyme isoprene synthase is responsible for its biosynthesis. Isoprene is also common in low concentrations in many foods. 15 µmol/kg/h, equivalent to approximately 17 mg/day for a 70 kg person. Its estimated production rate in the human body is. The United States Department of Transportation considers isoprene a hazardous material that needs to be marked, labeled, and transported with appropriate care.Īs noted above, isoprene is produced biologically in animals, plants, and humans. It can form explosive mixtures in air and is highly reactive, capable of polymerizing explosively when heated. Isoprene, however, can be a harmful environmental pollutant and toxicant when present in excess. About 95 percent of isoprene production is used to produce a synthetic version of natural rubber. Isoprene is also an important industrial chemical, being readily available as a by-product of the thermal cracking of naphtha or oil. Some natural rubber sources (called gutta percha) are composed of trans-1,4-polyisoprene, a structural isomer of the cis form, with similar but not identical properties. Typically, high-quality natural rubber also contains a few percent of other materials, such as proteins, fatty acids, resins, and inorganic materials. Natural rubber is a polymer of isoprene-most often cis-1,4-polyisoprene-with a molecular weight ranging from 100,000 to 1,000,000 daltons. It is formed naturally in animals and plants and is the most common hydrocarbon in the human body. At room temperature, purified isoprene is a highly flammable, colorless liquid that can be easily ignited. Isoprene is a common name for the chemical compound 2-methylbuta-1,3-diene. Except where noted otherwise, data are given for
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