Tyrosyl peptides

P. Gauduchon and P. Wahl, Pulse fluorimetry of tyrosyl peptides, Biophys. Chem. 8, 87-104 (1978). 

A number of studies on the fluorescence decay of tyrosine, tyrosine derivatives, and small tyrosyl peptides have been carried out. 36-38 Whereas the tyrosine zwitterion and tyrosine derivatives with an ionized a-carboxy group exhibited monoexponential fluorescence decay (x = 3.26-3.76 ns), double- or triple-exponential decay was observed in most other cases. As in the case of the tryptophan model compounds, the complex decay kinetics were again interpreted in terms of rotamer populations resulting from rotation around the C —Cp bond. There is evidence to indicate that the shorter fluorescence lifetimes may arise from rotamers in which the phenol ring is in close contact with a hydrated carbonyl group 36 37 and that a charge-transfer mechanism may be implicated in this quenching process. 39 ... 

Salman-Tabcheh, S., Rabgaoui, N., and Torreilles, J., Neutrophil-catalysed dimerisation of tyrosyl peptides. Free Radicals Res. Commun. 19,217—227 (1993). 

Fig. 19. Topography of the NBS cleavage of the six tyrosyl peptide links of native and

Aromatic amino acids can affect the shielding of aliphatic amino acids that are spatially close. The first such observation showed a high-held shift of the leucyl side chain resonances in the D-leucyl-tyrosyl peptide when compared to the shifts observed in the L-leucyl-tyrosyl diastereoisomer (Bovey and Tiers, 1959), which was attributed to greater proximity of the leucyl and tyrosyl side chains in the d-l pair. 

N-Terminal tryptophanyl peptide bonds are not cleaved by the action of NBS. The reason for the failure of the cleavage reaction may be related to the possibility that the free a-amino group of tryptophan derivatives and not the carboxamido function interact preferentially with the bromoindolenine. Similar amino group participation has been found with N-terminal tyrosyl peptides, which are not cleaved by NBS (434). 

ScHMiR, G., L. Cohen, and B. Witkop The oxidative Cleavage of Tyrosyl-Peptide Bonds. I. Cleavage of Dipeptides and Some Properties of the Resulting Spirodienone-Lactones. J. Amer. Chem. Soc. 81, 2228-2233 (1959). 

In mammalian cells, the two most common forms of covalent modification are partial proteolysis and ph osphorylation. Because cells lack the ability to reunite the two portions of a protein produced by hydrolysis of a peptide bond, proteolysis constitutes an irreversible modification. By contrast, phosphorylation is a reversible modification process. The phosphorylation of proteins on seryl, threonyl, or tyrosyl residues, catalyzed by protein kinases, is thermodynamically spontaneous. Equally spontaneous is the hydrolytic removal of these phosphoryl groups by enzymes called protein phosphatases. 

A peptide linker-chelate analog, glycyl-tyrosyl-lysine-N-e-DTPA (GYK-DTPA), was incorporated onto B72.3 antibody and labeled with 11 In and 90y.81,82 In vitro and in vivo evaluations in dogs were conducted. Results indicated that the 11 in chelate was stable in vivo however, the 90Y version showed a biphasic decay pattern. The covalent bond between the peptide and DTPA precluded use of one of the coordinating arms that is necessary to coordinate 90Y in a stable fashion. 

Figure 19.11 shows the conjugation of tyrosyl-lysine to KLH using various concentrations of EDC. The elution profile shows the gel filtration pattern resulting after the reaction. Progressive decrease in the peptide peak (peak 2) with increasing amounts of EDC correlates to... 

Figure 19.8 To study the conjugation of peptides to carriers using different levels of EDC, tyrosyl-lysine was conjugated to BSA and separated after the reaction by chromatography on a Sephadex G-25 column. As the EDC level was increased in the reaction, more peptide reacted and the peptide peak (the second peak) was depleted. The absorbance of the carrier peak (the first one) increases as more peptide is conjugated.

Figure 19.11 The EDC conjugation of tyrosyl-lysine to KLH is illustrated by the gel filtration pattern on Sephadex G-25 after the reaction. The first peak is the carrier protein and the second peak is the peptide. A blank containing no EDC is also shown to provide baseline peak heights that would be obtained if no crosslinking occurred. When more EDC was added, more peptide was conjugated, as evidenced by peptide peak depletion.

Figure 19.12 EDC conjugation reactions can be extraordinarily consistent using the same peptide crosslinked to two carrier proteins. This figure shows the gel filtration pattern on Sephadex G-25 after completion of the crosslinking reaction. Conjugation of tyrosyl-lysine to BSA and KLH are shown. The first peaks represent eluting carrier, while the second peaks are the excess peptide. Note the consistency of conjugation using the same levels of EDC addition.

S Guttmann, RA Boissonnas. Synthesis of benzyl V-acetyl-L-seryl-L-tyrosyl-L-seryl-L-methionyl-y-glutamate and related peptides, (side-chain alkylation) Helv ChimActa 41, 1852, 1958. 

R. W. Cowgill, Tyrosyl fluorescence in proteins and model peptides, in Biochemical Fluorescence Concepts 2 (R. F. Chen and H. Edelhoch, eds.), pp. 441 186, Marcel Dekker, New York (1976). 

J. B. A. Ross, W. R. Laws, A. Buku, J. C. Sutherland, and H. R. Wyssbrod, Time-resolved fluorescence and H NMR studies of tyrosyl residues in oxytocin and small peptides Correlation of NMR-determined conformations of tyrosyl residues and fluorescence decay kinetics, Biochemistry 25, 607-612 (1986). 

Thyroid epithelial cells synthesize and secrete T4 and T3 and make up the functional units of thyroid glandular tissue, the thyroid follicles. Thyroid follicles are hollow vesicles formed by a single layer of epithelial cells that are filled with colloid. T4,T3, and iodine are stored in the follicular colloid. T4 and T3 are derived from tyrosyl residues of the protein thyroglobulin (Tg). Thyroid follicular cells synthesize and secrete Tg into the follicular lumen. Thyroid follicular cells also remove iodide (I ) from the blood and concentrate it within the follicular lumen. Within the follicles, some of the tyrosyl residues of Tg are iodinated, and a few specific pairs of iodoty-rosyl residues may be coupled to form T4 and T3. Thus, T4, T3, and iodine (in the form of iodinated tyrosyl residues) are found within the peptide structure of the Tg that is stored in the follicular lumen. 

Several applications of photoreactive peptides require the presence of a radionuclide to allow specific and sensitive detection of the photo-cross-linked conjugates. In several cases, radioiodination of tyrosyl moieties and radiolabeled Bolton-Hunter reagents have been used. However, the presence of a radiolabel within the benzophenone photophore is desirable, particularly when the objective is to identify the site of photo-insertion of benzophenone. To this end some radiolabeled, benzophenone-based compounds have been developed and used in peptide synthesis, in particular tritiated Phe(4-Bz) (Scheme 24)J2161 [1-14C-carboxy]-4-benzoylbenzoic acid,1221 and 4-benzoyl-(2,3-3H2)-dihydrocinnamic acid.[154l In addition, 4-(4-hydroxybenzoyl)phenylalanine (Scheme 25) has been directly radioiodinated with Na125I and Chloramine-T)151 ... 

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... 

Iodination of PIR (147) showed 1 residue buried, Tyr 25, and all others iodinated at least to the monoiodotyrosyl form. Pepsin-inactivated RNase also has only one abnormal tyrosyl by titration which is thus assumed to be 25. Iodination of RNase-S is very similar to RNase-A in the early stages (lift). Extensive iodination leads to dissociation of the protein and peptide components. Direct iodination of S-protein indicated that all 6 tyrosyl residues were accessible, in this sense comparable to urea-denatured RNase-A. Substantial structural changes must be involved for both S-protein and PIR if Tyr 97, in particular, is to become susceptible to attack (see Section IV,B,3). 

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