Spectra tyrosine

First, it is possible to excite a chromophore corresponding to the active site, and detennine which modes interact with it. Second, by using UV excitation, the amino acids with phenyl rings (tryptophan and tyrosine, and a small contribution from phenylalanine) can be selectively excited [4], The frequency shifts in the resonance Raman spectrum associated with them provide infomiation on their enviromnent. 

Though a large number of small molecule inhibitors against a variety of tyrosine kinases are being developed, the most advanced drugs can be roughly classified as (i) Bcr-Abl/Src family kinase inhibitors, (ii) ErbB inhibitors and (iii) broad spectrum TfCIs with an anti-angiogenic component. 

Fig.S. Correlation between the integrated area of the seven line ESR spectrum (of Cu-H-Y, Cu-MCM-22 and Cu-VPl-5) and conversion of L-tyrosine, phenol, o-cresol and m-cresol (Curves A-D, respectively).

In the solid, dynamics occurring within the kHz frequency scale can be examined by line-shape analysis of 2H or 13C (or 15N) NMR spectra by respective quadrupolar and CSA interactions, isotropic peaks16,59-62 or dipolar couplings based on dipolar chemical shift correlation experiments.63-65 In the former, tyrosine or phenylalanine dynamics of Leu-enkephalin are examined at frequencies of 103-104 Hz by 2H NMR of deuterated samples and at 1.3 x 102 Hz by 13C CPMAS, respectively.60-62 In the latter, dipolar interactions between the 1H-1H and 1H-13C (or 3H-15N) pairs are determined by a 2D-MAS SLF technique such as wide-line separation (WISE)63 and dipolar chemical shift separation (DIP-SHIFT)64,65 or Lee-Goldburg CP (LGCP) NMR,66 respectively. In the WISE experiment, the XH wide-line spectrum of the blend polymers consists of a rather featureless superposition of components with different dipolar widths which can be separated in the second frequency dimension and related to structural units according to their 13C chemical shifts.63... 

Precursors of phenylpropanoids are synthesized from two basic pathways the shikimic acid pathway and the malonic pathway (see Fig. 3.1). The shikimic acid pathway produces most plant phenolics, whereas the malonic pathway, which is an important source of phenolics in fungi and bacteria, is less significant in higher plants. The shikimate pathway converts simple carbohydrate precursors into the amino acids phenylalanine and tyrosine. The synthesis of an intermediate in this pathway, shikimic acid, is blocked by the broad-spectrum herbicide glyphosate (i.e., Roundup). Because animals do not possess this synthetic pathway, they have no way to synthesize the three aromatic amino acids (i.e., phenylalanine, tyrosine, and tryptophan), which are therefore essential nutrients in animal diets. 

In the resonance Raman spectra of GO0X (125), vibrational modes have been assigned to both the tyrosinate ligand (Tyr 495) as well as the tyrosyl radical (Tyr 272). The spectrum does not provide evidence for the speculation that the tyrosyl radical is delocalized onto the jr-stacked tryptophan residue (Trp 290) (126, 127). Recent results of high-frequency EPR measurement (30) on the apogalactose oxidase radical are also consistent with the radical spin density being localized on the modified Tyr 272 moiety only. 

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

Histone HI from the fruit fly Ceratitis capitata has two tyrosine residues. Jordano et al.(<)2> have observed two differences from calf thymus HI (1) the apparent quantum yield does not increase on protein folding and (2) there is a pH- and conformation-dependent shoulder at 340 nm in the emission spectrum. This group has attributed this 340-nm emission to tyrosinate.(97) Their studies demonstrate that the folding of histone HI from C. capitata is pH and ionic strength dependent. The possibility of tyrosinate formation at neutral pH is discussed in greater detail in Section 1.5.2. 

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... 

In 1971, adrenodoxin, an iron-sulfur protein with a single tyrosine residue and no tryptophan was shown to fluoresce at 331 nm upon 280-nm excitation at neutral pH/20 1 On cooling from room temperature to 77 K, the emission maximum shifts to 315 nm. The redox state of the iron does not have any effect on the tyrosine emission. From these results, an exciplex between the excited singlet state of tyrosine and an unidentified group was suggested as the cause of the anomalous emission energy/2031 Later studies have shown that the excitation spectrum is a red-shifted tyrosine spectrum, that removal of the iron to form the apoprotein has no effect on the emission, and that heat, low pH, guanidine hydrochloride, urea, and LiCl all cause the emission... 

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. 

An additional emission band near 350 nm has been observed for lima bean trypsin inhibitor (LBTI).(173) The authors discussed both the possibility of contamination by tryptophan and excited-state tyrosinate formation. Since this 350-nm emission has a tyrosine-like excitation spectrum that is slightly shifted compared to that of the major 302-nm emission, it is also possible that the tyrosine residue in a fraction of the LBTI molecules could be hydrogen bonded. This model is supported by the observations that the phenol side chain is shielded from solvent and has an anomalously high pKa. 

J. Baudier and D. Gerard, The S-100b protein Tyrosine residues do not exhibit an abnormal fluorescence spectrum, J. Neurochem. 40, 1765-1767 (1983). 

Native fluorescence of a protein is due largely to the presence of the aromatic amino acids tryptophan and tyrosine. Tryptophan has an excitation maximum at 280 nm and emits at 340 to 350 nm. The amino acid composition of the target protein is one factor that determines if the direct measurement of a protein s native fluorescence is feasible. Another consideration is the protein s conformation, which directly affects its fluorescence spectrum. As the protein changes conformation, the emission maximum shifts to another wavelength. Thus, native fluorescence may be used to monitor protein unfolding or interactions. The conformation-dependent nature of native fluorescence results in measurements specific for the protein in a buffer system or pH. Consequently, protein denatur-ation may be used to generate more reproducible fluorescence measurements. 

Selenoprotein A is remarkably heat stable, as seen by the loss of only 20% of activity on boiling at pH 8.0 for lOmin (Thrner and Stadtman 1973). Although selenoprotein A contains one tyrosine and no tryptophan residues, it contains six phenylalanine residues and thus has an unusual absorbance spectrum (Cone et al. 1977). Upon reduction, a unique absorption peak emerges at 238 nm, presumably due to the ionized selenol of selenocysteine, which is not present in the oxidized enzyme. The activity of selenoprotein A was initially measured as its ability to complement fractions B and C for production of acetate from glycine, in the presence of reducing equivalents (e.g., dithiothreitol). Numerous purification schemes were adopted for isolation of selenoprotein A, all of which employed the use of an anion exchange column to exploit the strongly acidic character of the protein. 

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