Possible Interaction: Isoleucine and Tryptophan

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

“On the other hand, Ile and Leu ratios decreased ( Trp ; tryptophan, Tyr; tyrosine, Phe; phenylalanine, Ile; isoleucine, Leu; leucine, Val; valine).”

“Phenylalanine consistently reduced, and isoleucine slightly reduced the predictive value of the plasma tryptophan ratio.”

“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).”

“The concurrent administration of a large neutral amino acid (LNAA; valine or isoleucine ) with oral Trp , in high doses probably sufficient to compete with Trp for transport into gut cells, blocked the Trp-induced rise in urinary 5-HIAA.”

“ Abstract Isoleucine was found to be limiting for the growth of rats fed corn diets supplemented with lysine, tryptophan , valine, and threonine or 24% zein diets supplemented with most of the essential amino acids.”

“Replacement of any of the tryptophans of [Lys3]gA with isoleucine resulted in suppression of the pore-forming activity of the peptide, the effect being significantly dependent on the position of tryptophans.”

“This space is reduced in ALDH10s with low BADH activity, because an isoleucine (Ile) pushes the Trp against the Tyr.”

“Abstract Dietary isoleucine administered to weanling rats for 25–32 days reduces 5-hydroxylation of tryptophan by liver homogenates.”