Tryptophan

               I love turkey.  I love cranberry sauce that has the ridges from its can.  Most of all, I love stuffing.  Thanksgiving is a great food holiday!

                I bet we’ve all seen family members taking a Thanksgiving snooze after eating too much turkey.  (I’m sure Uncle Dave’s impromptu nap has nothing to do with the number of beers drunk while lying on the couch watching football…)  Many people feel that sleepiness following large Thanksgiving meals is due to the tryptophan found in the turkey.  A quick PubMed search of “tryptophan and sleep” will turn up 648 results.  Tryptophan does play a role in sleep.  However, tryptophan isn’t only found in turkey – it’s in egg, soybeans, cheddar cheese, chicken, beef, salmon and even bananas!  According to Snopes.com, you will not eat enough tryptophan on Thanksgiving to feel any appreciable effects, much like every other day of your life when you are ingesting many other foods that contain the molecule.  Also, most experts agree that the post-dinner fatigue is probably due to both an increase in metabolism and blood flow to your gastrointestinal tract.

                So… what is this little molecule?  What does it look like?  What else do we know about it?

                Figure 45.1 shows you what tryptophan looks like.  It’s a small molecule of carbon, nitrogen, hydrogen, and oxygen.  Most things in your body are made of the same four elements (although sometimes we throw in sulfur, phosphorous or a metal for fun).  You’ll notice that the left end of the molecule has two rings of atoms.  These rings are cool because it allows tryptophan to be fluorescent!  If you shine light of 280 nm on tryptophan, it will spit light back at you ranging from 300 – 350 nm.  

                Tryptophan is also something that you’ve heard me talk about in these posts before: it is an amino acid.  In fact, tryptophan is an essential amino acid.  What does that mean?  It means our body has no way of making it, so we must bring it into our bodies via our diets.  Our body needs amino acids to create proteins (oh, that pesky Central Dogma post just never goes away, does it?).  Of the 20 amino acid used to build proteins, 9 are essential.  We have the tools (enzymes, precursors) present in our cells to make all the non-essential amino acids, but essential ones must be ingested.  They are “essential” to our diet, if you will.  Without these amino acids, our bodies won’t make proteins properly and, subsequently, won’t run properly.  Do you remember Jurassic Park?  The dinosaurs were all unable to synthesize lysine (another amino acid).  Unless the animals’ diets were supplemented with lysine, they would die.  

                Interestingly, our bodies do have the tools to take tryptophan and turn it into other useful things.  For example, tryptophan will bind to the enzyme tryptophan hydroxylase and out will pop serotonin.  Serotonin is a neurotransmitter that is commonly thought to “make people feel happy.” 

                Serotonin can then, in turn, bind to N-acetyltransferase and be converted into another molecule that will bind to 5-hydroxyindole-o-methyltransferase and become melatonin.  This molecule is involved in our circadian rhythms.

                I will come back to tryptophan in the last post of the “From DNA to Protein” series, which will be posted soon.

                Until then...

Essential amino acid: Those amino acids that must be provided by our diets

Non-essential amino acid: those amino acids that our body can make

REFERENCES

http://www.snopes.com/food/ingredient/turkey.asp

Schaechter, JD and Wurtmann, RJ.  “Serotonin release varies with brain tryptophan levels.” (1990) Brain Research 532 (1-2) pgs 203 – 210

Wurtman, RJ and Anton-Tay, F. “The mammalian pineal as a neuroendocrine transducer.” Recent Prog. Horm. Res. 25, pgs 493 – 522.