Editor’s Note: The following section is technically complex, be ye forewarned.
Once the AI component of the analysis generates tightly-correlated groupings and matches them with competitive groupings, we have the three concentric layers of the DiscOmic system. At this point, we have groupings that make statistical sense, but no underlying biochemical theories that support the observed patterns. In order to add strength to the organizational scheme, we have developed underlying enzymological hypotheses for each of the three rings used in the DiscOmic system. Before we review how the data relates to enzymology in cannabis, let’s do a quick review of enzymology, biosynthesis, and genetics, and how all three relate.
An overview of how enzymes mediate reactions that occur during biosynthesis. Clockwise from top-left: A scheme for an anabolic enzyme that builds chemical bonds; a scheme for a catabolic enzyme that destroys chemical bonds; and an example of a biosynthetic enzyme-mediated pathway of limonene.
Here we see a quick overview of the mechanism of enzymes. Enzymes are either anabolic, meaning that they build bigger molecules by forming chemical bonds, or catabolic, meaning they break molecules down by cleaving chemical bonds. In fact many enzymes have activity of both anabolism and catabolism, but every enzyme must be a member of at least one of the two categories. By using combinations of these enzymes that target different bonds and different molecules, nearly any molecule imaginable can be constructed.
These linear biosynthetic pathways are the link between genetic information and physical traits. If a genome is a library, genes are like books, and each book is a set of instructions on how to build a specific enzyme or protein. Any physical difference in the enzyme will cause physical differences in molecules made by that enzyme. It is these differences in molecular structure that are the cause of the differences in physical traits in the whole organism.
The anabolic process can be thought of as a long assembly line, where each enzyme modifies a chemical bond and then passes the molecule to the next enzyme in the line. This is graphically represented as biosynthetic pathways, like the one illustrated above for limonene. Although humans, for simplicity of interpretation, like to represent the pathway to one molecule as a straight line, the truth is that many molecules are made from common precursors, causing our linear biosynthetic pathways to branch out. Inside the cells of an organism, these pathways happen in parallel at the same time, and the precursor reaction must produce enough precursor to distribute to all the enzymes.
If there is not enough precursor to keep every enzyme at full capacity, they compete for available precursors, often with the winners being faster reaction enzymes and the losers being slower reaction enzymes. To better illustrate the complexity of terpene biosynthesis and enzymology, we have constructed a biosynthetic mapping of terpenes and cannabinoids based on the research paper by Rodney Croteau published in 1987 on terpene synthesis.
6 Although Croteau’s paper did not perform experiments in cannabis plants, the terpene synthesis pathways examined were similar enough to create a biosynthetic landscape within which the enzymological analysis of cannabis could operate.
Map overview of the biosynthesis of terpenes in higher plants. The universal precursor, mevalonic acid pyrophosphate, can be seen in the top-left of the image. Arrows indicate enzymatic transformations and branch out in numerous directions to a variety of terpenes and intermediates. Colors from the DiscOmic system have been used to circle the major terpenes in each terpene group. Editor's Note: Click the thumbnail for a larger image.
The complexity and coordination involved in biosynthesis is evident in the above enzymological map. The highlighting of the major terpenes in each of DiscOmic’s terpene group illustrates the complexity of finding these patterns, and why the AI measures described above were necessary for establishing definite patterns. Because the enzymology of terpene synthesis is so complex, we will examine a biosynthetic map that focuses exclusively on the compounds of interest and their common precursors in order to better understand each DiscOmic terpene group.
Enzymology mapping of the relationship between the outer-ring groups 1 and 2. Intermediates illustrated as black circles, and enzymes are indicated in blue. Terpenes are indicated by major group color.
The first map, the sesquiterpenes (orange) vs. the pinenes (green) is a straightforward inverse relationship. The best way to chemically explain inverse statistical relationships is to describe a system with a common precursor and two competing enzymes. In this scheme the common precursor is labeled as precursor 1 (or P1). P1 is hypothesized to be geranyl pyrophosphate based on the available data.
6 Two enzymes, E1 and E2, compete for this precursor to generate intermediates that can either become pinenes or sesquiterpenes. Additional enzymes may mediate the distribution of terpenes within that group, such as E3 and E4 mediating P2, believed to be farnesyl pyrophosphate based on available evidence.
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Enzymological models such as this can easily explain the phenomenon where individual terpenes fail to have any correlation but show a strong correlation as a group. This would explain how the total of the group would be a more consistent number than the components, because the components of that group are all derived from a common precursor.
Enzymology mapping of the relationship between the middle-ring groups 4 and 3. Intermediates illustrated as black circles, and enzymes are indicated in blue. Terpenes are indicated by major group color.
The second map, the terpinenes (purple) vs. the limonene-linalool (yellow) is also a straightforward inverse relationship. Again, we hope to describe a system with a common precursor and two competing enzymes to explain the observed correlation. In this scheme the common precursor is labeled as precursor 1 (or P1). P1 is hypothesized to be linalyl pyrophosphate based on the available data.
6 Two enzymes, E1 and E2, compete for this precursor to generate intermediates that can either become terpinenes or limonene-linalool. Additional enzymes may mediate the distribution of terpenes within that group, such as E3 and E4 mediating P2, believed to be alpha-terpinyl pyrophosphate.
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Once again, we see a scheme where individual terpenes fail to have much correlation but show tight correlation as a group. The reasoning is based on the stable number of the total, contrasted with the more chaotic competing enzymes that do the “final touches” on terpene synthesis.
Enzymology mapping of the relationship between the inner-ring groups 6 and 5. Intermediates illustrated as black circles, and enzymes are indicated in blue. Terpenes are indicated by major group color.
The third map, ocimene (blue) vs. the myrcene (red) is also more complex relationship than was observed in the first or second map. Ocimene and myrcene are not inversely correlated, where the presence of one competes with the other, nor are they directly correlated, where the amount of one is tied to the amount of the other in a fixed ratio. This relationship shows no observable correlation, yet both terpenes are present at such high concentrations that they constitute a substantial portion of a cannabis sample’s terpene content. The lack of correlation between the two cannot be explained very easily, because both are known to be made through the precursor geranyl pyrophosphate.
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The best theory that fits the evidence at this time is that both ocimene and myrcene can be made from a common precursor, but each terpene can also be made from derivatives of that precursor.
6 Now if ocimene and myrcene are made from the exact same precursors, then we would see them in a fixed ratio. But, if ocimene and myrcene are able to interact with different derivatives of geranyl pyrophosphate, then it would allow two independent numbers to be derived from the same baseline value of precursor. What would influence the final number of these two terpenes would be a mixture of enzymes, some affecting the myrcene pathway, some the ocimene pathway, and many having distinct effects on both.
This degree of complexity is very common in enzymological schemes, especially in higher plants such as cannabis. With complications such as enzyme promiscuity, a phenomenon where one enzyme can actually cross-catalyze different reactions at different rates, these patterns can become even more challenging to understand. It is for this reason that tools for the consuming public, the cannabis industry, and the cannabis research community, are needed to help humans begin to benefit from the complexities of cannabis, even as the final aspects of our scientific understanding of the cannabis and human organisms are still being discovered.