Originally Posted by Conductor71
Yes, which leads back to why are our neuromelanin so vulnerable?
BTW, tried 500 mg of TH yesterday and felt great with no noticeable wear off. Today, it interfered with Sinemet absorption leaving me with two bad offs. Ths is a known, so how do we take it close enough to a Sinemet dose to benefit but far enough away so as not to interfere?
doesn't address tyrosine directly but interesting
i've always assumed we get more than enough tryrosine and it's precursors thru a normal diet. how much Phenylalanine and tyrosine is in a glass of milk, 4oz of steak, an egg, etc? if the body didn't have a way iof controlling how these amino acids got into a brain and/or were converted in the brain to neurotransmitters, wouldn't eating a steak nearly kill us? just saying AA metabolism in the brain is very complicated, especially with active transport shuttling these aa''s across the brain barrier?
The essential amino acids cannot be synthesized by the brain and, therefore, must be supplied from protein breakdown and diet. Phenylalanine, leucine, tyrosine, isoleucine, valine, tryptophan, methionine and histidine, which are essential amino acids, and also the precursor of dopamine, L-DOPA, enter the brain as rapidly as glucose. These amino acids are transported into the brain by the leucine-preferring or the L-type transport proteins. These compounds compete with each other for entry into the brain. Therefore, an elevation of plasma level of one will inhibit uptake of the others. This competition may be important for certain metabolic diseases such as phenylketonuria (PKU), where high levels of phenylalanine in plasma reduce brain uptake of other essential amino acids.
Small neutral amino acids, such as alanine, glycine, proline and GABA (gamma-aminobutyric acid), are markedly restricted in their entry into the brain. These amino acids are non-essential amino acids and are transported by alanine-preferring or A-type transport protein. The A-type transport protein is not present on the luminal surface of the blood brain barrier. In contrast, these small neutral amino acids appear to be transported out of the brain across the blood-brain-barrier.