Possible Interaction: Leucine and Tryptophan

“Other large neutral amino acids, namely valine, isoleucine, leucine and phenylalanine affect precursor availability by competing with tryptophan and tyrosine for the transport system across the blood brain barrier.”

“Adding extra tryptophan to the high leucine diet tended to negatively affect daily gain (p = 0.081) and feed conversion ratio (p = 0.074).”

“Brain concentrations of tyrosine, phenylalanine and tryptophan were significantly reduced in animals receiving supplements of leucine for two and six weeks.”

“ L-leucine was found to interfere with tryptophan and nicotinic-acid metabolism, and leucine supplements induced " black tongue " (the canine equivalent of pellagra) in dogs.”

“Amino acids, such as valine, isoleucine and leucine compete with tyrosine and tryptophan for transport into the brain and might thus affect the central serotonin and catecholamine patterns.”

“In addition, significant inhibition of the apical-tobasolateral permeation of Trp by Leu and Phe was observed.”

“Fasting plasma tryptophan (TRP) levels and ratios of total … five large neutral amino acids (LNAAs)--tyrosine, phenylalanine, leucine, … tryptophan for passage across the blood-brain barrier were found to be significantly lower in a … major depression compared with 29 normal subjects and 21 patients with obsessive-compulsive disorder (OCD).”

“Brain uptake of tryptophan is regulated in part by competition from other plasma amino acids, e.g. leucine.”

“The other major factor that is thought to influence the levels of brain tryptophan is the concentration of the other neutral amino acids ( leucine , isoleucine, valine, tyosine and phenylalanine) which compete with tryptophan for transport into the brain (Fernstrom & Wurtman, 1972).”

“Azaserine, l-2,4 diaminobutyric acid, l-histidine, and l-leucine , at low concentrations, increase the initial velocity of uptake of l-tryptophan but compete with l-tryptophan at high concentrations.”