Tyrosine configuration

FIGURE 7 Tyrosine-derived poly(iminocarbonates) used to evaluate the effect of various side chain configurations on the physicomechan-ical properties of the resulting polymers. 

Solvent-cast films of tyrosine-derived polyiminocarbonates and polycarbonates were virtually indistinguishable in appearance and exhibited similar morphological features. When examined by X-ray diffraction, using an automated Scintag Pad V diffractometer all tested films were found to be completely amorphous. The lack of ordered domains in solvent-cast films seemed to be a general feature of tyrosine-derived polyiminocarbonates and polycarbonates, irrespective of the pendent chain configuration of the monomeric dipeptide. 

Figure 16.3 Conceptual illustration of two peptides before (left) and after (right) a chemical reaction with formaldehyde. The amino acids are represented as circles. In this particular peptide, a tyrosine (Y) is located within the epitope (shaded circles). An arginine (R) is located elsewhere in the peptide. Formaldehyde results in the formation of a covalent bond between the two residues, due to a Mannich condensation reaction, as shown on the right. The new configuration prevents antibodies from binding to the epitope on the left. 

Figure 1.5. Newman projections about the C —bond, showing the possible positions of the phenol group (R) in relation to the C substituents. The rotamer assignments I, II, and III and the corresponding values of the torsion angle Xi are indicated for tyrosine (and its derivatives) of the l configuration.

Fig. 8.15. Domain structure of Abl tyrosine kinase. The functionally characterized domains of Abl tyrosine kinase are shown in hnear configuration. NTS, nuclear localization signal.

The integrins do not have any enzyme activity in their own cytoplasmic domain, but on hgand binding, stimulation of tyrosine phosphorylation is observed on the cytoplasmic side of many cells, such as fibroblasts and platelets. The exact configuration of protein-protein interactions on the cytosolic side of the integrins is not clear and the mechanism of stimulation of protein tyrosine kinases is unknown. Some components of the focal adhesion points, such as the structural protein tensin, have SH2 and SH3 domains that may serve as specific attachment points for tyrosine kinases and other signal proteins. 

At alkaline pH values, even though no observable association or aggregation occurs, some changes in configuration are observed. Changes in the Cotton effect between 250 and 300 nm and in optical rotatory dispersion occur at pH 11.5. The fourth tyrosine, which was somewhat buried at neutral pH values, reacts with cyanogen fluoride at pH 10.0 and above (Gobrinoff 1967). 

Zyzzya genus [58]. The structure of prianosin A (= discorhabdin A) (52), including its absolute configuration, was unequivocally defined by X-ray analysis [54], while those of discorhabdins B (54) and D (57) were based on spectral data. The previous structures proposed for prianosins C and D [55] were revised to 2-hydroxydiscorhabdin D (56) and discorhabdin D (57), respectively [59]. A plausible biosynthetic pathway for these compounds suggests the involvement of a-amino acids tyrosine (C-l-N-9) and tryptophan (C-10-C-21) [55]. 

Intramolecular interactions between two coordinated amino acids can influence the position of-cis trans equilibrium. These interactions can take the form of hydrophobic stacking interactions, as observed between the side chains of tyrosines in [Cu(L-TyrO)2J and [Pd(L-TyrO)2], or Coulombic attraction between oppositely charged side chains, as in [Cu(HisO)L] (L = Arg, Lys or ornithine).51 The optical configuration of the amino acids is of particular importance for these interactions. For amino acids of the same configuration trans geometry (15) is required, but for amino acids of opposite configuration cis geometry (14) is necessary around the metal centre. 

The binding constant of the substrate acetyl-L-leucyl-L-tyrosine methylamide to pepsin (Km) is reported as 2.7 mM and the binding of the inhibitor acetyl-D-tyrosyl-D-leucine methylamide (Kt) as 5.8 mM. The binding shown in Fig. 6 was proposed for the reason that both binding constants are almost identical. This assumption is based upon the idea that the space-filling structure of leucyltyrosine in the L-configuration is similar to that of the reversed sequence, tyrosylleucine, in the D-configuration. A... 

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