Absorption spectra tyrosine

Muller et al.understand better the role of tyrosine in the structure and biological function of MDH. Resolution of the protein absorption spectrum, using iV-acetylphenylalanine ethyl ester in dioxane and A-acetyltyrosine ethyl ester in dioxane or 0.1 M phosphate buffer to model the effect of the local environments of the chromophoric groups, indicated that both the pig and the... 

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-... 

Most proteins have a broad characteristic absorption spectrum centered at about 280 nm. The major absorption is due to the presence of aromatic moieties in the amino acids phenylalanine, tyrosine, and tryptophan. During the a-lactalbumin purification described in this experiment, you will monitor the process by measuring the absorption at 280 nm (A2S0) of column fractions to be sure the experiment is proceeding correctly. You must recognize that you are measuring not the concentration or presence of a-lactalbumin specifically but the total amount of all proteins present. 

UV-Visible Absorption Spectrum Absorption spectroscopy Tyrosine-Tryptophan environments, presence of absorbing ligands or impurities. ... 

Ribonuclease contains no tryptophan. The absorption near 280 nm is almost entirely resulting from the 6 tyrosine residues. The ionization of tyrosine produces a marked shift to longer wavelengths in the absorption spectrum. The ionization can be monitored near 295 nm. Shugar (293) was the first to point out the abnormal behavior of 3 of the tyrosine residues on alkaline titration. Three titrate normally with apparent pK values near 10, but three do not titrate until much more alkaline pH values have been reached and irreversible alkaline de-naturation has set in. Some typical spectra and difference spectra are... 

Absorption spectrum is the plot of light intensity as a function of wavelength. Figure 1.2 shows the absorption spectra of tryptophan, tyrosine, and phenylalanine in water. A strong band at 210-220 nm and a weaker band at 260-280 nm can be seen. 

Absorption spectrum of ai-acid glycoprotein displays two peaks at 225 and 278 nm (Figure 2.3). This feature is characteristic for all proteins. The peak at 278 nm originates from the three aromatic amino acids of the proteins, tyrosine, tryptophan, and phenylalanine. The e for a protein is generally calculated at 278 nm. 

The additional effects in the aromatic region of the difference spectrum (250-300 nm) are probably caused by aromatic transitions which are influenced by the redox state of the copper. The shoulder at 270 nm, which occurs in all three proteins, could result from an increase in tyrosine absorption. In this context, it is interesting to recall that Tyr 108 (azurin numbering), which is relatively close to the proposed copper ligands Cys 112 and Met 121, is completely invariant both in azurin and plastocyanin and may therefore be an obligatory constituent of the copper site. 

Fig. 16. Spectroscopic characterization of the oxidized apogalactose oxidase free radical, (a) Optical absorption spectrum for the radical-containing apoprotein, (b) X-band EPR spectrum of the metal-free protein following Ir(IV) oxidation, (c) Expansion of the region near g = 2 comparing experimental data (Exp) with a theoretical simulation (Sim) based on coupling of the unpaired electron spin with one and one Hp proton of a tyrosine phenoxyl. Simulation parameters g = 2.0017, g2 = 2.0073 Ai Ha) = 8.4 G, A2(Hc,) = 8.8 G di(Hp) = 12.7 G, A2(Hp) = 13.8 G.

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. 

The part of a molecule that absorbs the light and is, therefore, responsible for its colour (whether in the visible or UV region) is called the chromophore, and the wavelength dependence of the absorption defines its absorption spectrum. Figure 7-3 illustrates the absorption spectrum of the three aromatic amino acids tryptophan, tyrosine and phenylalanine. 

The absorption spectrum of protein is maximum at 280 nm due to the presence of tyrosine and tryptophan, which are the strongest chromophores in that region. Hence the absorbance of the protein at this wavelength is adapted for its determination. 

The potential advantages of selective nitration of tyrosyl residues in native proteins are numerous. The reaction is performed under mild conditions, giving rise to a 3-nitrotyrosyl derivative (pK 7), which in the acid form absorbs intensely at 350 nm. Hence, the nitrotyrosine content may be readily determined spectrophotometrically, as well as by amino acid analysis ( 2.2.3). The absorption spectrum of 3-nitro-tyrosine is highly sensitive to solvent polarity and exhibits significant optical activity in the long wavelength absorption band. Consequently, nitrotyrosyl residues can be utilized as indicators of conformational change, or of interactions of proteins with other macromolecules or small molecules (e.g. Kirschner and Schachman 1973). Any perturbation in the pK of nitrotyrosyl residues is readily determined spectrophotometrically. 

The visible absorption spectrum of a solution containing a known concentration of nitrated protein is measured in a solution buffered at pH 9.0, and the absorbance at the maximum (near 428 nm) used to calculate the nitrotyrosine content ( 428nm for the nitrophenoxide ion is 4200). The tyrosine and nitrotyrosine content of the modified protein should also be determined by amino acid analysis. If the sum of these values does not add up to the tyrosine content of the unmodified protein, intra- or intermolecular cross-linking may have occurred. The amino acid analysis may also reveal whether other side-reactions have taken place. Particular attention should be paid to the half-cystine, cysteine, methionine, histidine and tryptophan contents of the modified proteins. Polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate offers a rapid and highly sensitive way of detecting products of intermolecular cross-linking. Such products are readily removed by gel filtration. 

Thus, knowledge of the transition moment direction of a phenol band could help in interpreting the fluorescence spectrum of a tyrosine chromophore in a protein in terms of orientation and dynamics. The absorption spectrnm of the first excited state of phenol was observed around 275 nm with a fluorescence peak aronnd 298 nm in water. The tyrosine absorption was reported at 277 nm and the finorescence near 303 nm. Fluorescent efficiency is about 0.21 for both molecules. The fluorescent shift of phenol between protic and aprotic solvents is small, compared to indole, a model for tryptophan-based protein, due to the larger gap between its first and second excited states, which resnlts in negligible coupling . ... 

Controlled reaction of G. gouldii hemerythrin with tetranitromethane has shown that tyrosyl residues 8 and 109 and, to a lesser extent, tyrosyl 67 are protected from nitration in the iron-protein (201—202). The more readily nitrated residues, namely tyrosines 18 and 70 are, hence, likely to he on the surface of the monomer. This partial modification did not affect either iron-binding, as judged by its visible absorption spectrum,... 

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

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