Isoprene synthesis by plants and animals.

Isoprene is emitted from both plants and animals at significant rates. There is evidence for a specific enzyme, isoprene synthase, that produces isoprene from dimethyl allyl pyrophosphate, one of the intermediates involved in the synthesis of higher-order isoprenoids such as cholesterol, carotenoids and monoterpenes (for example, pine scent). The role of isoprene in animals is unknown, but there is recent evidence that isoprene helps protect plant membranes involved in photosynthesis from thermal damage. Isoprene emission from plants is a natural process that contributes more hydrocarbon to the atmosphere than all of the anthropogenic hydrocarbons.