Tryptophanyl-tryptophan

Glycyl glutamic acid Glycyl proline Glycyl tryptophan Leucyl glycyl phenylalanine Tryptophanyl alanine Tryptophanyl glycine Tryptophanyl tryptophan Tryptophanyl tyrosine... 

The six major proteins of milk, asl-, o s2-, and /c-casein, jS-lactoglobulin, and a-lactalbumin, contain at least one tryptophan residue [57], the fluorescence of which allows the monitoring of the structural modifications of proteins and their physicochemical environment during the coagulation processes. Emission fluorescence spectra of the protein tryptophanyl residues were recorded for the milk coagulation kinetics induced by... 

The most direct demonstration of triplet-triplet energy transfer between the aromatic amino acids is the ODMR study by Rousslang and Kwiram on the tryptophanyl-tyrosinate dipeptide.(57) Since the first excited singlet state of tyrosinate is at lower energy than that of tryptophan, it is possible to excite tyrosinate preferentially. The phosphorescence of this dipeptide, however, is characteristic of tryptophan, which is consistent with the observation that the triplet state of tyrosinate is at higher energy than that of tryptophan, making tryptophan the expected triplet acceptor. 

Attenuation. A major mechanism of feedback repression, known as attenuation, depends not upon a repressor protein but upon control of premature termination. It was first worked out in detail by Yanofsky et al. for the trp operon of E. coli and related bacteria.184 186 Accumulation of tryptophan in the cell represses the trp biosynthetic operon by the action of accumulating tryptophanyl-tRNATlP, which specifically induces termination in the trp operon. Other specific "charged" arnino-acyl-tRNA molecules induce termination at other amino acid synthesis operons. 

L-Tryptophan (3) and L-tryptophanyl peptides are oxidatively cleaved by C6H5I-(OAc)2 to 3-(methoxymethyl)-l//-indole (4).2... 

Fig. 13. Schematic view of the oligopeptide succinyl-L-tryptophanyl-L-tryptophan bound between two deoxyhemoglobin A molecules in the crystal lattice. Broken lines indicate hydrogen bonds and dotted lines van der Waals contacts. The protein-ligand interactions include oxygen-aromatic interactions involving leucine-96 and an aromatic-aromatic interaction involving phenylalanine-4lfl. Reproduced with permission from Perutz el al. (1986).

The analytical method proposed by Pajot (1976) involves (a) incubating the protein of a known concentration in 6 M guanidine at pH 6.5-7 in the presence of 30 mM 2-mercaptoethanol for 30 min (if only a small amount of the protein is available, the incubation can be carried out directly in the fluorescence cuvette) and (b) measuring the fluorescence, excited at 295 nm and observed at 354 nm, yielded by the denatured protein in 6 M guanidine hydrochloride (tryptophanyl residues concentration 3-10 /xM). A linear calibration curve is obtained, thus allowing the free tryptophan fluorescence equivalents of the protein sample to be estimated by extrapolation. 

The other amino acid residue present in proteins that is susceptible to oxidation is the indole moiety of tryptophan (Fig. 11). The reducing potential of tryptophan is considerably less than that of cysteine and methionine, so oxidation of tryptophanyl residues usually does not occur until all exposed thiol residues are oxidized. Also, the spontaneous oxidation of tryptophanyl residues in proteins is much less probable than that of cysteinyl and methionyl residues. Tryptophan residues are the only chromophoric moieties in proteins which can be photooxi-dized to tryptophanyl radicals by solar UV radiation, even by wavelengths as long as 305 nm (B12). Tryptophanyl residues readily react with all reactive oxygen species, hypochlorite, peroxynitrite, and chloramines. Oxidative modifications of other amino acid residues require use of strong oxidants, which eventually are produced in the cells. Detailed mechanisms of action of these oxidants is described in subsequent sections of this chapter. 

Chicken egg white lysozyme (LZM) does not possess exposed methionyl residues, and it has six tryptophan residues, three of which, located at positions 62,108, and 111 are readily oxidizable with ozone and are built-in the LZM active center (D14). Tryptophanyl residues are also the first reacting moieties upon treatment of LZM with the MPO-Cr-H2C>2 system (at pH 4.5). The reaction occurs in several stages. In the first stage, which occurs when 1.4-1.8 mol of H2O2 for 1 mol of LZM is used, LZM loses its enzyme activity, but no derivative distinguishable from the native protein on the polyacrylamide gel electrophoresis is formed. The inactivation may be prevented by addition to the reaction medium A-acetylcysteine or... 

Bovine chymotrypsinogens A and B have the same NHrterminal residue, namely half-cystine. Both are activated by trypsin at about the same rate. The best technique thus far available for differentiating chymotrypsins A and B is to determine their activities on acetyl-L-tryptophan ethyl ester in the presence of 80% methanol (1). Table II shows that the much lower activity of chymotrypsin B on tryptophanyl esters is due to a stronger depressing effect of methanol (106). 

Recently, 2-(2-nitrophenylsulfenyI)-3-methyl-3-bromoindolenine (BNPS-skatole) has replaced N-bromosuccinimide, which had been used frequently in earlier studies. At low reagent to protein tryptophan ratios, in 50% aqueous acetic acid, BNPS-skatole reacts selectively with tryptophan residues converting these to the oxindole derivative. Methionine is concommitantly converted to the sulfoxide. At high concentrations of reagent, slow selective cleavage (to the extent of 15-60%) of the peptide bonds involving tryptophanyl residues is... 

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