and 349, each with a specific level of GPCR pathway activation. And
odorant Z may bind to olfactory receptor proteins 9, 45,91, 112, 136,
138, 149, 207, 298, and 333, each with a particular level of activation.
And so on. Thus, it becomes possible to discriminate a very, very, very
large number of odorant molecules according to their different pat-
terns of activation of the 350 olfactory GPCRs.
One measure of the importance we place on olfaction is the economic
success of the perfume industry. Billions of dollars are spent every
year purchasing perfumes. Commercial perfumes are mixtures of
many aromatic molecular components. Such aromatics were origi-
nally derived exclusively from natural materials, mostly from plants.
These days, most commercial perfumes use numerous synthetic
molecules to replace the harder-to-obtain and more precious mate-
rials from plants and animals. Though great effort is made to mimic
complex natural aromas by these methods, necessarily some of the
nuance is lost. Artisan perfumers continue to follow the old ways of
mixing perfumes using only aromatic essences from plant and animal
materials.
The old ways. The way of perfume. The way of plant medicines. The
term essential oil designates the oily concentrate of aromatic mole-
cules from a plant. Essential (Latin esse = to be) refers to the distinctive
scent of the plant, its hallmark aroma, its spirituous essence and
quintessence. Frequently the essential oil includes many of a plant’s
medicinal qualities. It is oily because the aroma-carrying molecules
frequently are hydrophobic. Essential oils are often prepared by
distillation, the process of heating an extract of the plant and con-
centrating the more volatile components. Distillation was invented a
thousand years ago by Arab alchemists—primarily to make perfumes
and to concentrate preparations from medicinal plants (Fig. 12.2).