Tyrosine polar

The pH dependence of the CIDNP effect for the amino acids Trp, His and Tyr is shown in Figure 13. The tyrosine polarization is fairly constant over a wide pH range and decreases in the range where the phenolic OH-group is ionized (pK = 10.3). This probably does not reflect lower activity towards the triplet flavin at pH > 10, however. 

Rather a change in mechanism from H-abstraction to electron transfer seems to be involved, since strong tyrosine polarizations have been observed for proteins at pH II (21). 

In polar solvents, the structure of the acridine 13 involves some zwitterionic character 13 a [Eq. (7)] and the interior of the cleft becomes an intensely polar microenvironment. On the periphery of the molecule a heavy lipophilic coating is provided by the hydrocarbon skeleton and methyl groups. A third domain, the large, flat aromatic surface is exposed by the acridine spacer unit. This unusual combination of ionic, hydrophobic and stacking opportunities endows these molecules with the ability to interact with the zwitterionic forms of amino acids which exist at neutral pH 24). For example, the acridine diacids can extract zwitterionic phenylalanine from water into chloroform, andNMR evidence indicates the formation of 2 1 complexes 39 such as were previously described for other P-phenyl-ethylammonium salts. Similar behavior is seen with tryptophan 40 and tyrosine methyl ether 41. The structures lacking well-placed aromatics such as leucine or methionine are not extracted to measureable degrees under these conditions. 

Rachel, K., Asuncionpunzalan, E. and London, E. (1995) Anchoring of tryptophan and tyrosine analogs at the hydrocarbon polar boundary in model membrane-vesicles - paralax analysis of fluorescence quenching induced by nitroxide-labelled phospholipids. Biochemistry 34,15475-15479. 

On the other hand, in accord with the free radical mechanism peroxynitrite is dissociated into free radicals, which are supposed to be genuine reactive species. Although free radical mechanism was proposed as early as in 1970 [111], for some time it was not considered to be a reliable one because a great confusion ensued during the next two decades because of misinterpretations of inconclusive experiments, sometimes stimulated by improper thermodynamic estimations [85]. The latest experimental data supported its reliability [107-109]. Among them, the formation of dityrosine in the reaction with tyrosine and 15N chemically induced dynamic nuclear polarization (CIDNP) in the NMR spectra of the products of peroxynitrite reactions are probably the most convincing evidences (see below). 

Small side chains (SSC) =glycine+alanine+serine, Polar chains (PC) =aspartic acid+threonine+serine+glutamic acid+tyrosine+lysine +histidine+arginine. 

Asakura, T., Ohgo, K., Ishida, T., Taddei, P., Monti, P., and Kishore, R. (2005). Possible implications of serine and tyrosine residues and intermolecular interactions on the appearance of silk I structure of Bombyx mod silk fibroin-derived synthetic peptides High-resolution 13C cross-polarization/magic-angle spinning NMR study. Biomacromolecules 6, 468-474. 

Weber G. (1960) Fluorescence Polarization Spectrum and Electronic Energy Transfer in Tyrosine, Tryptophan and Related Compounds, Biochem. J. 75, 335-345. 

Since the oxidative polymerization of phenols is the industrial process used to produce poly(phenyleneoxide)s (Scheme 4), the application of polymer catalysts may well be of interest. Furthermore, enzymic, oxidative polymerization of phenols is an important pathway in biosynthesis. For example, black pigment of animal kingdom "melanin" is the polymeric product of 2,6-dihydroxyindole which is the oxidative product of tyrosine, catalyzed by copper enzyme "tyrosinase". In plants "lignin" is the natural polymer of phenols, such as coniferyl alcohol 2 and sinapyl alcohol 3. Tyrosinase contains four Cu ions in cataly-tically active site which are considered to act cooperatively. These Cu ions are presumed to be surrounded by the non-polar apoprotein, and their reactivities in substitution and redox reactions are controlled by the environmental protein. 

Plastocyanin from parsley, a copper protein of the chloroplast involved in electron transport during photosynthesis, has been reported to have a fluorescence emission maximum at 315 nm on excitation at 275 nm at pH 7 6 (2°8) gjncc the protein does not contain tryptophan, but does have three tyrosines, and since the maximum wavelength shifts back to 304 nm on lowering the pH to below 2, the fluorescence was attributed to the emission of the phenolate anion in a low-polarity environment. From this, one would have to assume that all three tyrosines are ionized. A closer examination of the reported emission spectrum, however, indicates that two emission bands seem to be present. If a difference emission spectrum is estimated (spectrum at neutral pH minus that at pH 2 in Figure 5 of Ref. 207), a tyrosinate-like emission should be obtained. 

Gaudet, E.A., Huang, K.S., Zhang, Y., Huang, W., Mark, D., and Sportsman, J.R., A homogeneous fluorescence polarization assay adaptable for a range of protein serine/threonine and tyrosine kinases, ]. Biomol. Screen., 8,164, 2003. 

Synthesized tyrosine-, phenylalanine-, tetrahydroisoquinoline-, tetralin- and tryptophan analogs Chirobiotic R Reversed-phase mode H20/Me0H Polar organic mode MeOH/HOAc/TEA 269... 

Tyrosine (Tyr or Y) (4-hydroxyphenylalanine ((5)-2-amino-3-(4-hydroxyphenyl)-propanoic acid)) is a polar, neutral, aromatic amino acid with the formula H00CCH(NH2)CH2C6H50H and is the precursor of thyroxin, dopamine, norepinephrine (noradrenaline), epinephrine (adrenaline), and the pigment melanin. Being the precursor amino acid for the thyroid gland hormone thyroxin, a defect in this may result in hypothyroidism. Tyr is extremely soluble in water, a property that has proven useful in isolating this amino acid from protein hydrolysates. The occurrence of tyrosine- 0-sulfate as a constituent of human urine and fibrinogen has been reported. ... 

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