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Geraniol is an acyclic, ten-carbon primary alcohol with molecular formula ${\mathrm{C}}_{10}{\mathrm{H}}_{18}\mathrm{O}$. Its carbon skeleton contains two double bonds and a terminal hydroxyl group. It is chemically distinct from geranyl diphosphate, the activated diphosphate ester of that alcohol.^[ref]

A 2004 study by Yoko Iijima and colleagues connected this structure to a plant reaction. They purified geraniol synthase activity from leaf glands of sweet basil and showed conversion of geranyl diphosphate into geraniol. Expression of the identified gene produced an enzyme with similar activity.^[ref]

The motivating mechanistic experiment used isotope labelling. Supplying water containing oxygen-18 led to oxygen-18-labelled geraniol. That result tracked the origin of the product's oxygen and supported a synthase-type mechanism rather than simple removal of phosphate groups by a phosphatase.^[ref]

The distinction is experimentally powerful: two proposed routes can yield the same unlabelled product yet predict different atom origins. Measuring how much geraniol appears answers a yield question; locating the label addresses a mechanistic question. The isotope observation complements product identification rather than replacing it.

Geraniol synthase converts geranyl diphosphate and water into geraniol and diphosphate. The accepted IUBMB name is geranyl diphosphate diphosphatase, EC 3.1.7.11. That classification describes the overall reaction; it does not on its own identify every bond-breaking step in the mechanism.^[ref]

In a 2004 study, Yoko Iijima and colleagues purified activity from sweet-basil leaf glands. The plant enzyme produced geraniol from geranyl diphosphate, and expression of the identified gene yielded a catalyst with similar activity.^[ref]

The key mechanistic test supplied water containing oxygen-18. Label appeared in geraniol, supporting a route in which cleavage produces a geranyl cation that is captured by water. Merely observing unlabelled geraniol would not distinguish this from a route retaining the substrate's original alcohol oxygen.^[ref]

An ideal isolated conversion of $2\mu \mathrm{mol}$ substrate produces two micromoles each of geraniol and diphosphate. Product amount checks stoichiometry, while isotope labelling tests atom origin. These measurements answer different questions, even when both support the same net reaction. The synthase name should not be read as implying that ATP is required by this specific conversion.

Yoko Iijima is the first author of a 2004 study characterizing geraniol synthase from aromatic leaf glands. The work connected purification of the plant enzyme with expression in Escherichia coli, where the encoded protein reproduced the geraniol-forming activity.^[ref]

The team used isotope labelling to test mechanism. Water containing oxygen-18 supplied the oxygen incorporated into geraniol, detected through a mass shift by mass spectrometry. That observation distinguished the tested synthesis route from simple removal of a phosphate group while retaining the substrate's original oxygen.^[ref]

Producing the same final molecule does not establish that two catalysts use the same route. Tracing the origin of an atom adds mechanistic information beyond identifying the product. The expression comparison separately linked the isolated gene sequence to the measured enzyme activity.