I want to understand how amino acids are absorbed and used in the body. In another post of yours I read about larger AAs being absorbed and crowding out smaller ones (or something like that). Also, lysine and arginine being antagonists (may not be the exact right word).
Yes, that is the right word. Basically certain amino acids share the same binding sites for absorption. And the larger ones in these groups will crowd out the smaller ones blocking their absorption. For example phenylalanine shares the same biding sites with tyrosine and tryptophan and being the largest can interfere with the absorption of the others. Arginine and lysine are also examples. The reason that lysine is used to treat herpes outbreaks is because arginine triggers herpes outbreaks and lysine is an arginine antagonist.
So.......... what exactly is the difference in taking an AA as a supplement as opposed to comsuming foods high in that AA? Can food sources be beneficial?
There is really little difference between the two. Of course the AA supplements will have a higher AA content, but this does not mean more beneficial. The body is only capable of absorbing and utilizing a small amount of amino acids each day. About 30g or 3 ounces of amino acids. The excess is waste material that will have to be broken down then eliminated as urea.
Although as I pointed out the amino acids are grouped that share specific binders. So a single large amino acid will not block the block the absorption of all other amino acids. In addition there is the factor of how much of any one amino acid is present since there are a specific number of receptors. If the one amino acid is not locking up all of the receptors for that group then there will be receptors available for the absorption of other amino acids in that group.
Also keep in mind that some amino acids are produced by the body from other amino acids.
What is the consequence of taking a supplement with more than one AA? I'm sure it would depend on the mix
It is not so much as whether the supplement has other amino acids as it is if there is excessive amounts of a certain amino acid since this can block absorption. For example you can take a small amount of bee pollen, which has all the amino acids. But the absorption will not be inhibited since there are a sufficient number of receptors to absorb all the amino acids. If you take a protein drink in conjunction with it though then there may be more amino acids than available receptors and the larger amino acids will win out. This is why it is so important to take individual amino acids on an empty stomach at least 30 minutes before meals when using amino acid therapy.
Any general information would be fantastic and I am also thinking specifically about the AAs that are converted to neurotransmitters.
Some amino acids are converted in to neurotransmitters, but not all.
So using targeted amino acid(s) in a supplement simply utilises all of the receptors without competitive inhibition.
Pretty much. Unless you take very large amounts though all the receptors will not be be utilized, just a certain percentage of them.
Thinking about neurotransmitter precursors...You mention that tryptophan and tyrosine share a binding site. So is it not a good idea to supplement these at the same time?
In small amounts there will be plenty of receptors to allow absorption of both. If you take them with a protein source though, such as a steak dinner then absorption can be inhibited due to the high level of amino acids.
Is that why one would use 5HTP or is that due only to its abilty to cross into the brain.
5-HTP is actually preferred because the conversion of tryptophan in to 5-HTP, then to serotonin is very poor.
Just out of interest.. are the larger amino acids required in greater amounts for protein synthesis?
No, even the smallest amino acid glycine is required for the synthesis of some proteins. So size does not matter.