Plant Enzymes Synthesize Essential Oil Constituents

Introduction
 

Essential oils from different plants can vary tremendously in terms of chemical composition, even when the plants are closely related. For instance, even though all fir tree essential oils contain the same nine terpene compounds, Siberian Fir is almost entirely composed of bornyl acetate, camphene, and alpha-Pinene, while Douglas Fir is mainly composed of beta-Pinene, sabinene, and terpinolene. So what makes different plants produce different chemical compounds? And why is it that closely related species share the same chemical diversity but vary so greatly in chemical dominance? These two phenomena can be explained using the genetics, molecular biology, and biochemistry of terpene synthase enzymes.

Plant Enzymes

If you’ve ever taken a biology course, you know that enzymes are giant biomolecules that catalyze chemical reactions. Synthases are a class of enzymes that synthesize larger molecules from smaller building blocks. Terpene synthases make terpenes and terpenoids, the compounds that constitute essential oils.

In chemistry you probably learned that a mixture of reactants can form multiple products depending on the reaction conditions. The purpose of an enzyme is to control the exact chemical conditions at the active site, which is the part of the enzyme responsible for holding onto the reactants, transferring chemical bonds, and stabilizing transition states. Even the most miniscule change in an enzyme’s structure can make it favor the formation of one product in higher amounts compared to the other products.

A single terpene synthase enzyme can actually produce a mixture of different terpenes. The DNA sequence coding for a terpene synthase enzyme varies between species, even when they are close relatives. Since proteins are made using the DNA code, slight genetic differences result in a slightly different protein sequence, affecting the shape and therefore the catalytic properties of the terpene synthase.
 

Diversity in Terpene Synthases

Take 1,8-cineole synthase for example. In a recent study, researchers isolated 1,8-cineole synthase from wild thyme plants and studied its biochemical properties.¹ They compared their findings to prior research on other 1,8-cineole synthase enzymes taken from other plants. Although most of the enzymes studied share greater than 80 percent similarity of their amino acid sequences, their catalytic activity varies immensely. The version of the 1,8-cineole synthase taken from plants from the Solanaceae family makes seven monoterpenes: 1,8-cineole, limonene, myrcene, beta-Pinene, alpha-Pinene, sabinene, and alpha-Terpineol. These seven compounds together are known as the “cineole cassette.”¹ The 1,8-cineole synthase taken from Pinaceae plants, on the other hand, doesn’t produce the full cineole cassette. It doesn’t make limonene and sabinene, but instead produces gamma-Terpinene. Another 1,8-cineole synthase from Lavandula x intermedia only produces three of the seven compounds in the cassette (sabinene, alpha-Terpineol, and limonene) and it makes an additional compound, beta-phellandrene.¹

Of course, 1,8-cineole synthase is only one specific type of terpene synthase. Over 5,000 different kinds of terpene synthase proteins have been characterized, and a single species of plant can express hundreds of different terpene synthases at a time. The inter-species diversity in terpene synthases explains the nearly infinite chemical diversity of essential oils.

Conclusion

Because of the incredible chemical diversity between species, the pure essential oil from a specific plant has a unique and highly complex chemical composition that cannot be replicated synthetically, nor by blending essential oils from similar plants. In fact, GC/MS testing reveals a unique chemical fingerprint for every different essential oil. At doTERRA, one portion of our CPTG^® quality testing process involves obtaining the chemical fingerprint of our essential oil, and making sure it matches our standard of pure, natural, and unadulterated essential oil. Thanks to the complexity of plant enzymes and the hard work done by doTERRA’s analytical chemists, you can know for certain that your essential oils are the highest quality available on the market.

Bibliography
 

• Learn about the chemistry of Douglas Fir essential oil.
   
• Read about essential oil cellular activity.