Tryptophan peptides with

Reaction with N-Bromosuccinimide (MBS). The behaviour of 2-sul-fenylated-tryptophan peptides towards NBS is of particular interest, since NBS can be used to modify this amino acid residue in proteins (see Section III.2.1.). In the following scheme, the reactions occurring upon treatment of a 2-sulfenylated tryptophan peptide with NBS are shown. Bromination at the 3-position of the indole moiety is followed by displacement of the halogen atom by the carbonyl function of the side chain amide, with concomitant cyclization to an imido-lactone (165). 

Amines, Amino acids, peptides, e g tryptophan, tryptamine, peptides with terminal tryptophan groups... 

The highly regioselective hydrolysis of tryptophan-containing peptides with the [Pd(en)]2+ (en = H2NC2H4NH2) complex has been reported by Kostic and co-workers.436 The hydrolysis does not proceed without the palladium(II) complex. However, when equimolar amounts of a... 

CNTs can be functionalized with protein via non-covalent bond (Li et al., 2005 Kim et al., 2003 Mitchell et al., 2002). For example, (beta-lactamase I, that can be immobilized inside or outside CNTs, doesn t change enzyme s activity (Vinuesa and Goodnow, 2002). Taq enzyme can attach to the outside of CNT, and doesn t change its activity (Cui et al., 2004). Peptide with Histidine and Tryptophan can have selective affinity for CNT(Guo et al., 1998). Monoclonal antibody can attach to SWNTs. Protein-modified CNTs can be used to improve its biocompatibility and biomolecular recognition capabilities (Um et al., 2006). For example, CNTs functionalized with PEG and Triton X-100 can prevent nonspecific binding of protein and CNTs. Biotin moiety is attached to the PEG chains Streptavidin can bind specifically with biotin-CNT (Shim et al., 2002). 

Detection of peptides in HPLC can be achieved by measuring natural absorbance of peptide bonds at 200-220 nm. Unfortunately at these wavelengths a lot of food components and also the solvents used for analysis absorb, demanding an intensive sample pretreatment and clean-up [129]. Peptides with aromatic residues can be detected at 254 nm (phenylalanine, tyrosine, and tryptophan) or 280 nm (tyrosine and tryptophan). Taking advantage of the natural fluorescence shown by some amino acids (tyrosine and tryptophan), detection by fluorescence can also be used for peptides containing these amino acids [106]. 

Under these reducing conditions of hydrolysis of tryptophan peptides, cystine is reduced to cysteine and its coelution with proline using standard buffer gradients, makes quantitation difficult. Thus, cysteine and cystine are generally derivatized prior to acid hydrolysis by oxidation to cysteic acid with performic acid 21 or alkylation, upon reduction in the case of cystine, with iodoacetic acid 21 or, more appropriately, with 4-vmylpyridine)22 23 50 Conversion of cysteine into 5- 3-(4-pyridylethyl)cysteine bears the additional advantage of suppressing epimerization via the thiazoline intermediate, thus allowing for standardization of the acid-hydrolysis dependent racemization of cysteine in synthetic peptides)24 ... 

Peptides are usually detected by absorbance at between 200 and 220 rnn at concentrations of between 100 and 1000 ng (80). Since many solvents and even other components in the samples absorb at these wavelengths, samples must be carefully purified, and the solvents used must be transparent to ultraviolet light. Detection of peptides with aromatic amino acids (Phe, Tyr, Trp) can be carried out at 254 rnn if tyrosine or tryptophan is present, detection at 280 nm is feasible. In some cases detection has been carried out at 230 nm (59). 

The function of the leader sequence is to fine tune expression of the trp operon based on the availability of tryptophan inside the cell. It does this as follows. The leader sequence contains four regions (Fig. 2, numbered 1-4) that can form a variety of base-paired stem-loop ( hairpin ) secondary structures. Now consider the two extreme situations the presence or absence of tryptophan. Attenuation depends on the fact that, in bacteria, ribosomes attach to mRNA as it is being synthesized and so translation starts even before transcription of the whole mRNA is complete. When tryptophan is abundant (Fig. 2a), ribosomes bind to the trp polycistronic mRNA that is being transcribed and begin to translate the leader sequence. Now, the two trp codons for the leader peptide lie within sequence 1, and the translational Stop codon (see Topic HI) lies between sequence 1 and 2. During translation, the ribosomes follow very closely behind the RNA polymerase and synthesize the leader peptide, with translation stopping eventually between sequences 1 and 2. At this point, the position of the ribosome prevents sequence 2 from interacting with sequence 3. Instead sequence 3 base-pairs with sequence 4 to form a 3 4 stem loop which acts as a transcription terminator. Therefore, when tryptophan is present, further transcription of the trp operon is prevented. If, however, tryptophan is in short supply (Fig. 2b), the ribosome will pause at the two trp codons contained within sequence 1. This leaves sequence 2 free to base pair with sequence 3 to form a 2 3 structure (also called the anti-terminator),... 

Fig. 10. Highly schematic representation of the orientation of several tryptophan-containing peptides with respect to calmodulin. (A) With tryptophan in position 1, the indole is located on the hydrophilic side of the helix and is exposed to solvent. Peptides with tryptophan on this face of the helix should exhibit emission maxima near that of indole in water ( 350 nm), a small anisotropy, and a high accessibility for acrylamide quenching. (B) In position 2, the tryptophan is partially exposed at the interface between the peptide and calmodulin. Peptides with a tryptophan in this location should have fluorescence properties that are intermediate between example A and C. (C) The tryptophan is on the hydrophobic side of the helix and is almost entirely buried. The emission maximum should be strongly blue-shifted, the anisotropy should be large, and the accessibility to acrylamide quenching low. Taken from O Neil et al. (1987).

Ternary complex kalata B7/Mn2+/ DPC micelle Cyclotide varv F AcAMP2-like peptide with phenylalanine 18 mutated to tryptophan... 

The improved DNA binding and condensation provided by amino acids such as tryptophan suggests that the inclusion of hydrophobic interactions within DNA complexes may be beneficial. Peptides with moities that provide cooperative hydrophobic behavior of alkyl chains of cationic lipids would improve the stability of the peptide-based DNA delivery systems. Two general classes of lipopeptide analogs of Tyr-Lys-Ala-Lysn-Trp-Lys peptides have been prepared by including a hydrophobic anchor. The general structures are N, N-dialkyl-Gly-Tyr-Lys-Ala-Lysn-Trp-Lys and Na,Ne-diacyl-Lys-Lysn-Trp-Lys. These peptides differ from the parent structures in that they self-associate to form micelles in aqueous solutions. The inclusion of dialkyl or diacyl chains in the cationic peptides improves the peptide ability to bind DNA and reduces aggregation of the complexes in ionic media. 

The participation of an isolated double bond in a five-membered ring in displacement reactions is apparently difficult or impossible, but fortunately becomes very easy when the double bond is conjugated with an imino group and in the 7,5-position relative to a carboxamido group, as in tryptophan peptides. 

However the NBS titration method apphed to TMV protein (A-protein) led to a decrease of optical density at 280 m t commensurate with only 1.9 moles of tryptophan per mole of protein of molecular weight 18,270. After the reaction of 6 moles of NBA per TMV protein subunit 0.2-0.3 mole each of alanine and lysine were released as new NH2-terminal residues. The so-called I-peptide with 3 moles of NBA per mole of tryptophan in 66 % acetic acid or with 3 moles of NBS per mole of tryptophan in aqueous 0.2... 

The study of the interaction of peptides with proteins by optical spectroscopy is greatly facilitated if the peptide contains tryptophan and the protein does not, as in the case of the calmodulin/peptide systems studied here. Even for proteins which contain one or more tryptophans this approach can still be used provided that the spectral changes associated with binding of the peptide are sufficiently large. The use of synthetic peptides or site specific mutagenesis allows almost any residue to be replaced by tryptophan. The most conservative substitutions on the basis of size and hydrophobicity would be Phe -> Tip or Tyr -> Tip. 

Malencik and Anderson have described a series of studies, using various probe strategies, on the interaction of peptides with calmodulin. Because calmodulin does not contain tryptophan, they were able to observe the increase in the anisotropy of tryptophan in various peptides on binding. For example, the anisotropy from the tryptophan of Polistes mastparan, a toxic peptide from the social wasp, on excitation at 294 nm, increased from around 0.02 to 0.13 on binding to calmodulin. In another study Malencik and Anderson characterized the association of melittin,... 

Structural determination of the ComX pheromone synthesis studies on ComXRO-E-2 pheromone and ComXRO-E-2 peptides containing modified tryptophan residue with a geranyl group 07Y608. 

Figure 16.38- Schemade of the inteiactlona of the a-hetical MLCK peptide with calioodutin. The position of the single tryptophan residue is moved along the helix in 16 synthetic peptides. Reprinted, with permission. from O Neil, K. T., Wolfe, H. K, EricksM-Viitanen, S., and OeOrado, W. F. Fluorescence properties of calmodulin-binding peptides reflect alpha-helieal periodicity, Science 236 1454-1456, Copyright O 1987, American Association for the Advancemeat of Science.

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