Tyrosine ultraviolet absorption

A number of investigators have studied the effect of ozone on the ultraviolet absorption spectra of proteins and amino acids. A decrease in the absorption of 280-nm light in a number of proteins was originally reported ly Giese et aV to be a consequence of ozone exposure they suggested that this was due to an interaction of ozone with the ring structures of tyrosine and tryptophan. Exposure of a solution of tryptophan to ozone resulted in a decrease in 280-nm absorption, whereas the extinction coefficient of tyrosine increased. Similar results with tyrosine were reported by Scheel et who also noted alterations in the ultraviolet spectra of egg albumen, perhaps representing denaturation by ozone. 

Amino acids do not give any very useful ultraviolet absorption spectra unless they possess aromatic groups as in phenylalanine, tryptophan, and tyrosine. The absorption characteristics of these groups are more useful in monitoring chemical and conformational changes in proteins than they are in the simple amino acids. 

Ultraviolet absorption spectra of tryptophan (Trp), tyrosine (Tyr), and phenylalanine (Phe) at pH 6. The molar absorptivity is reflected in the extinction coefficient, with the concentration of the absorbing species expressed in moles per liter. (Source From D. B. Wetlaufer, Adv. Protein Chem. 17 303-390, 1962.)... 

A solvent which has been foimd to be of great interest in connection with protein conformation studies is ethylene glycol. Sage and Singer (1958, 1962) have investigated in some detail the properties of RNase in pure ethylene glycol, containing added neutral electrolyte. They examined the ultraviolet absorption spectrum, the ionization behavior of the tyrosine residues by spectrophotometric titration experiments, and the optical rotatory dispersion of the system. 

Ultraviolet Absorption The ultraviolet absorption characteristics of the aromatic side chains of the primary amino acid sequence are often used to estimate an extinction coefficient for a protein. The extinction coefficient is calculated based upon the number of tyrosine, tryptophan, and phenylalanine (aromatic) residues in the protein. Phenylalanine has a relatively weaker absorptivity and may not be included in the calculations. One advantage of this approach is the fact that it is relatively nondisruptive, leaving protein conformation undisturbed. In addition, the same solution used for the concentration assessment can be removed from the cuvette and used for additional experiments. The measurement is based upon Beer s law ... 

Electronic (ultraviolet) absorption spectrum of L-tyrosine, at pH 12.55 the logarithm of the absorbance, i , is plotted against wavelength. 

For human serum albumin Tanford (1950) found by spectrophotometry that the ionization of the tyrosine hydroxyl groups was completely reversible up to pH 12. Measurements at the wavelength of the tyrosine anion maximum (2930 A.), uncorrected for the small tryptophan contribution, gave a pK of 11.7 for this process. Both the ultraviolet absorption and titration data for this protein could be quantitatively interpreted on the basis of complete freedom of all the 18 tyrosine hydroxyl groups in the molecule to ionize. In this respect human serum albumin thus resembles insulin and not ovalbumin. 

Figure 1.7. Absoqition spectra of tiyptophan, tyrosine and phenylalanhi Wctbufcr, D. B., 1962, Ultraviolet absorption spectra of proteins and a Protein Ghent. l7.303-39a...

Fig. 2. Ultraviolet absorption spectra of tryptophan, tyrosine, and phenylalanine at pH 6 (from Wetlaufer >).

Fig. 6. Ultraviolet absorption spectra of phenylalanine and tryptophan (a) and tyrosine (pH 7 and pH10)(b)...

Fig. 1.5. Ultraviolet absorption spectrum of tyrosine as affected by pH. (according to Luebke, Schroeder and Kloss, 1975) — 0.1 mol/1 HCl, — 0.1 mol/1 NaOH...

The ultraviolet absorption spectra of arachin, associated species (820 14.6) and dissociated species (820° 14.6 and 9.5) in phosphate buffer at pH 7.3 and 11.0, are identical (65). This agrees with ultracentrifugal data that the two species are equilibrium states of the same molecule. The ultraviolet absorption spectra of arachin and conarachin at pH 7.3 are similar however, at pH 11.0 the spectra are very different. The data indicate that if conarachin, the slower sedimenting species, results from the dissociation of arachin, the dissociation takes place in such a manner that conarachin has a lower percentage of tyrosine than arachin. 

Side chains of the three aromatic amino acids phenylalanine, tyrosine, and tryptophan absorb ultraviolet light in the 240- to 300-nm region, while histidine and cystine absorb to a lesser extent. Figure 3-13 shows the absorption spectrum of a "reference compound" for tyrosine. There are three major absorption bands, the first one at 275 nm being a contributor to the well-... 

The aromatic amino acids phenylalanine, tyrosine, and tryptophan all possess absorption maxima in the near-ultraviolet (fig. 3.7). These absorption bands arise from the interaction of radiation with electrons in the aromatic rings. The near-... 

Tyrosine is one of the important a-amino acids and is oxidatively polymerized with tyrosinase to melanin, the black pigment in animals [25-30], Melanin plays a role in the prevention of damage to the organism that occurs through the absorption of ultraviolet light. Melanin is the only major paramagnetic organic com-... 

The ultraviolet spectra of many proteins exhibit small shifts of absorption maxima to shorter wavelengths and small decreases in extinction coefficient at these maxima when the native conformations are disrupted in aqueous solution (see Beaven and Holiday, 1952 Beaven, 1961 and the article by Wetlaufer in this volume). These effects are presumably due to the special environments in which chromophoric side chains, particularly those of tyrosine and tryptophan, find themselves within the native protein molecule as compared to the free chromophores in aqueous solutions. The special properties of these native environments have been attributed variously to hydrogen bonding, particularly of tyrosine residues (Scheraga and Laskowski, 1957), vicinal electrical effects, including ion-... 

The absorption of ultraviolet light by proteins at wavelength 280 nm is caused mostly by the amino acids tyrosine and tryptophan along the protein molecular chains. The molecular absorption coefficients for these two amino acids are ... 

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