Tyrosine phenolic hydroxyl

The solvent pH and polarity will affect the absorbance and fluorescence properties of a protein. A notable example of pH effects on absorbance is seen with tyrosine residues, where a change in pH from neutral to alkaline results in a shift of the absorbance maximum to a longer wavelength and an increase in absorptivity due to dissociation of the tyrosine phenolic hydroxyl group (Freifelder, 1982 Fasman, 1989). An example of solvent polarity effects on fluorescence is observed with tryptophan, where a decrease in solvent polarity... 

The tyrosine phenolic hydroxyl function was readily methylated to form a methyl ether under aqueous conditions at pH 10 with the proteins... 

Additional Evidence of Tyrosine Phenolic Hydroxyl Group Binding in... 

Diode array detection is a useful tool for identification of phosphotyrosine-containing peptides as phosphorylation of the tyrosine phenolic hydroxyl causes a hypsochromic shift in the UV spectra from 275 to 266 nm (41). 

The phenolic hydroxyl group of tyrosine, the imidazole moiety of histidine, and the amide groups of asparagine and glutamine are often not protected in peptide synthesis, since it is usually unnecessary. The protection of the hydroxyl group in serine and threonine (O-acetylation or O-benzylation) is not needed in the azide condensation procedure but may become important when other activation methods are used. 

The 4-(dimethylaminocarbonyl)benzyl ether has been used to protect the phenolic hydroxyl of tyrosine. It is stable to CF3CO2H (120 h), but not to HBr/AcOH (complete cleavage in 16 h). It can also be cleaved by hydrogenolysis (H2/Pd-C). ... 

Several such polymers have by now been prepared and were found to possess a variety of interesting material properties. Tyrosine-derived poly(iminocarbonates) (see Sec. IV) would be a specific example. These polymers were synthesized by means of a polymerization reaction involving the two phenolic hydroxyl groups located on the side chains of a protected tyrosine dipeptide (12). 

Figure 1. Molecular structures of Bisphenol A and fully protected tyrosine dipeptide. The amino and carboxylic acid groups of the dipeptide are rendered unreactive by protecting groups (schematically represented by X and Y). This leaves the phenolic hydroxyl groups as the only reactive sites of the molecule.

In general, phenolic hydroxyl groups in complex molecules, which could not be esterified by the usual methods, were smoothly acylated with imidazolides. For example, a cyclohexapeptide containing two tyrosine groups reacts with 3,5-dinitrobenzoyl-imidazole to give a 95% yield of the crude bis-3,5-dinitrobenzoate.[20]... 

Ionization of the phenol hydroxyl group in tyrosine shifts the 277-nm absorption peak to 294 nm and the 223-nm peak to 240 nm. The molar extinction coefficient for the peak of the lower energy band increases from about 1350 M l cm-1 to about 2350 M em-1 and for the higher energy band from about 8200 M cm-1 to about. 1,000 M l cm-1.113 141 In addition, the lower energy absorption band of tyrosine shows vibrational structure that is lost upon ionization of the phenol side chain. 

Hydrogen bond between the phenolic hydroxyl group of tyrosine and another molecule containing a carbonyl group. 

Ultraviolet difference spectra have frequently been used to measure the ionization of the phenolic hydroxyl of tyrosines. The sulfydryls of cysteines and the imidazoles of histidines are also amenable to difference spectroscopy. 

Cleavage of terminal tyrosyl and tryptophanyl peptides. L-Tyrosyl-L-alanine (1) and related dipeptides are cleaved by 01 1(0Ac)2 in CH3OH containing KOH to 4-(methoxymethyl)phenol (2) and an amino acid. Under the same conditions, L-tyrosine yields (4-hydroxyphenyl)acetonitrile, HOC6H4CH2CN. The phenolic hydroxyl group and the free amino group are essential for this cleavage.1... 

Cyanuric fluoride has been used to modify tyrosine residues, substituting the phenolic hydroxyl group. A maximum of 3 residues in RNase was found to react at pH 10.9 and 25° (148a). However, some mystery surrounds this number, as with other estimates of accessibility, since alkaline-denatured material where all tyrosine residues are available still showed the reaction of only 3 residues with cyanuric fluoride. However, similar observations have been made on iodination in 8 Af urea (11 )- At pH 9.3, Takenaka et al. (149) found that only 2 residues reacted and that 115 was not one of them. Two more reacted after alkali denaturation. Two were resistant under all conditions tested. No enzymic activity data were reported. 

The distribution of values of the equatorial angle is not determined by intrinsic geometric considerations, and all possible values of are equally probable. However, unfavorable spatial overlap of electron orbitals determine the observed distribution of the variable . Thus, the distribution of values of is nearly uniform over its entire range (0° < < 360°) with the following notable exceptions The presence of the Cp—Cy bond in tyrosine, phenylalanine, and tryptophan makes values of = 0° unlikely, and = 180° in tyrosine is partially blocked by the phenolic hydroxyl group. Finally, the five-membered ring of tryptophan partially blocks values of between 180° and 360°. 

---