Tyrosine histidine competition

In another test of tyrosine-histidine competition, samples of synthetic valyl-hypertensin were oxidized with three equivalents of NBS at pH values... 

There are three caveats when one forms structural hypotheses on the basis of the observed CIDNP signals. First, the polarization intensity of a residue is not simply a constant that is specific for that particular amino acid but is subject to a Stem-Volmer competition of all accessible residues for the excited dye molecules, so CIDNP of an accessible amino acid can be suppressed by other accessible amino acids that are more reactive that problem is most pronounced for histidine. Second, in one study surface accessibility as detected by CIDNP was found to depend not only on the location of the amino acid but also to some extent on the nature of the dye " no systematic investigation of this effect with a range of known protein structures has yet been attempted. Third, the radical cation of a tr)q3tophan or tyrosine residue could undergo electron transfer with a nearby tyrosine or tr)q)tophan that is located in the interior of the protein. If this pair substitution causes polarizations of the inner residue to develop, misinterpretations as to the protein structure might obviously result. This problem has attracted considerable attention. ° For lysozyme, such an intramolecular electron transfer appears to be more important in the denatured state than in the native state. ... 

High concentrations of blood phenylalanine result in increased uptake of phenylalanine into the brain and concomitant dcCTease in the uptake of other large neutral amino adds (LNAA). Phenylalanine is transported into the brain by one of the LNAA carriers, the 1. -amino add transporter 1 (LAT-1) [45 8]. This transporter also selectively transports the amino adds valine, isoleucine, methionine, threonine, tryptophan, tyrosine, and histidine. The binding of the LNAA to the LAT-1 transporter is a competitive process the rate of transport is proportionate to the blood concentration of all the transported amino acids [49]. This system has the highest affinity for phenylalanine, which in case of its high concentration in the blood, significantly decreases the transport of other LNAA and more phenylalanine is transported into the brain. By influence on the activity of tyrosine and tryptophan hydroxylases, elevated brain phenylalanine concentrations also negatively impact the synthesis of catecholamines and serotonin in the brain due to the altered metabolism of tyrosine and tryptophan [4]. 

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