Both Doug and I enjoyed John Burdett's recent Asian thriller Bangkok 8, set guess where. (It has weird sex, snakes. and revenge! What more do you need?) Anyway, one of the subplots in the book deals with the Asian amphetamine trade. This is not a matter of guys with bad teeth setting up trailers in the middle of nowhere. Well, OK, it is, but instead of manufacturing the crank from scratch, in Asia they extract a precursor from local Ephedra shrubs first. Which brings me to the real point of this post, phytochemistry! The Ephedra are weird-looking shrubs, sometimes called the joint-firs in English. You can see why. Ephedra itself is a living fossil, one of only three (maybe four) surviving genera of the gnetophytes, until recently thought to be the closest living relatives of the flowering plants. Ephedra have been found from the Cretaceous period, over 65 million years ago. They also have a remarkably odd biochemistry: they produce cyclopropyl amino acids. This may require some explanation.
Amino acids are the building blocks of all proteins. There are twenty principal amino acids, which you can find mention of in all the textbooks, and a whole bunch more of modified ones, for which you have to dig around a little more. Now, a protein is a polymer, like a plastic. Every protein molecule consists of chains of amino acids stuck together, like Legos. How do they manage this? Every amino acid has an acidic end and a basic end. During protein synthesis, the acidic end of one amino acid is made to react with the basic end on another, and voila! a bond is formed, and the protein increases in length by one more amino acid. Sounds complicated? It is. But it's a precise and accurate and surprisingly robust system. However, there are certain points where it can be jammed. Somewhere along the line, Ephedra evolved the ability to synthesize amino acids that contain carbon rings with only three atoms: cyclopropyl groups. This is weird, because this stresses the chemical geometry of the carbon atom almost to its limit. It's not particularly easy for organic chemists to do. And Ephedra does this on a bulk basis. It appears that Ephedra has evolved this as a form of chemical defense. Large amounts of these variant cyclopropyl amino acids are produced, up to 0.5% of the plant's dry mass. These amino acids are taken up by organisms that use the plant as food. But these variant amino acids, similar in affinity but crazily different in structure to everyday amino acids, gum up the parasite/herbivore's amino acid metabolism, in effect poisoning them in the midst of plenty. They die. Oh the embarrassment. (In fact, one species of Ephedra is called Ephedra antisyphilitica, although its anti-spirochete action has never been confirmed.) Except that's not all. Because evolution reuses its biochemistry, it turns out that the common amino acid glutamic acid (or glutamate, same as in MSG) is also a neurotransmitter. Would it surprise you that Ephedra also synthesizes cyclopropyl analogs to glutamate? While they jam up very specific glutamate receptors in vitro, the neurological effects of these chemicals on humans are unknown. As a completely separate matter, some species of Old World Ephedra also can also be up to 2% its dry mass in ephedrine or pseudoephedrine, compounds chemically very similar to methamphetamine. Hence their use as starting material in illegal synthesis. However, in New World Ephedra, those compounds are barely detectable in the plant, thus the different style of trailer labs alluded to above. However (again), a common name for North American Ephedra is "Mormon tea" , which suggests some sort of stimulant action is going on, which brings us back to the unknown neurological effects I mentioned before. Finally, going back to my previous post on paleoecology, the gnetophytes were once much more common than they are now. The genus Ephedra itself dates back to the Cretaceous. It seems likely that its peculiar biochemistry dates back that far as well. What I'd like to know is, what were the selective pressures which caused Ephedra to evolve this complicated biochemistry in the first place? Or, to put it another way, was Ephedra originally dinosaur crank?  This may require some explanation for those three eastern European readers who have read this far. The Mormons are a religous group, mainly found in the American West, who abstain from all caffeinated beverages!!! Apparently, some of them were willing to drink tea made from a living fossil instead. Many Mormons also believe in something much like the first series of Battlestar Galactica, but with Jewish American Indians taking the place of Lorne Greene and killer robots. I don't say it's related to their abstention. I don't say that at all.