Amino-acid residues tryptophan

Figure 2.2. The structure of a segment of a polypeptide chain (a) and of the amino acid residue tryptophan (b). Rotations are possible around the bonds with dihedral angles

The acid carboxypeptidase from A. saitoi releases the carboxyterminal phenenylalanine-amide (-Phe-NH2) from the carboxy-terminal amidated peptides, such as gastrin-related peptide (/-amyloxycarbonyl (Aoc)-Trp-Met-Asp-Phe-NH2, Aoc-WMDF-NH2) and molluscan cardioexcitatoiy neuropeptide (Phe-Met-Arg-Phe-NH2, FMRF-NH2) [86], The summarized data are shown in Table 12. When gastrin-related peptide was used as a substrate, the enzyme acted only as a carboxyamidase, because of the presence of the hydrophobic amino acid residue, tryptophan, in the P3 [12] position. 

Blakesley, V. A., Kato, H., Roberts, C. T., Jr., and LeRoith, D., Mutation of a conserved amino acid residue (tryptophan 1173) in the tyrosine kinase domain of the IGF-I receptor abolishes autophosphorylation but does not eliminate biologic function, /. Biol. Chem., 270[6], 2764, 1995. 

Two amino acid residues, tryptophan and methionine, have unique codons—UGG and AUG, respectively. All other amino acids may be coded for by more than one codon, such that the code is said to be degeuerate. This degeneracy is not uniform, but varies according to the particular amino acids. For example, three amino acids (arginine, leucine, and serine) have six codons, five amino acids have four, isoleucine has three, and nine amino acids have two. The first two letters of each codon provide the primary determinant in the specificity. For example, the codons for amino acid valine are GUU, GUC, GUA, and GUG. The open reading frame of the mRNA, which extends from the AUG codon to the termination codon, establishes the protein that is to be synthesized. 

Changes of the UV spectra of the samples at 280 nm (Fig. 2) point to active interaetion between ozone and aromatic amino acid residues (tryptophane. 

One of the main advantages of CE over gel electrophoresis is that the separation is monitored by online, on-column, or end-column detection. In the most frequently employed UV absorption photometric detection, a small part (less than 1mm) of the capillary serves as a detection cell. Micromolar concentrations of proteins are detectable using the low UV detection wavelength of 200-220 nm. A higher sensitivity, up to nanomolar concentrations, is achieved with fluorescence, particularly laser induced fluorescence (LIE) detection. The disadvantage of the LIE detection of proteins is the necessity for their derivatization using a fluorogenic label. The native fluorescence of proteins, mostly due to the presence of aromatic amino acids residues, tryptophan, and tyrosine, can be utilized only when low UV laser... 

Inhibitors of Bowman-Birk types are widely distributed in plants and significantly different from the Kunitz inhibitor in their amino acid composition and are able to interact not only with trypsin, but with chymotrypsin (Valueva Mosolov, 2002 Rawlings et al., 2004). Inhibitors of Bowman-Birk type characterized by the presence of two reactive centers on a single polypeptide chain rich in cysteine (7 or more residues in one polypeptide), and the lack of amino acid residues tryptophan and tyrosine. The molecular weight of such inhibitors can vary from 8 to 16 kDa. Sometimes there are inhibitors that contain two domains on one polypeptide chain and active only in relation to one type of enzyme (Valueva Mosolov, 2002 Yan et al., 2009 Mosolov Valueva, 2008). 

RNase Bovine ribonnclease A, an enzyme 124 amino acid residues. Note diat RNase lacks tryptophan. 

Histone H3 Histones are DNA-binding proteins found in chromosomes 135 amino acid residues. Note die very basic nature of this protein dne to its abmidance of Arg and Lys residues. It also lacks tryptophan. 

FIGURE 5.6 Bovine pancreatic ribonuclease A contains 124 amino acid residues, none of which are tryptophan. Four intrachain disulfide bridges (S—S) form cross-links in this... 

Concerning the Ca2+-triggered luminescence of obelin, Deng et al. (2001) reported an interesting observation (Fig. 4.2.2) the luminescence of the recombinant obelin from O. longissima is blue (7max 475 nm), whereas a mutant of this obelin, in which the amino acid residue-92 has been changed from tryptophan to phenylalanine, emits... 

Neurotoxins present in sea snake venoms are summarized. All sea snake venoms are extremely toxic, with low LD5Q values. Most sea snake neurotoxins consist of only 60-62 amino acid residues with 4 disulOde bonds, while some consist of 70 amino acids with 5 disulfide bonds. The origin of toxicity is due to the attachment of 2 neurotoxin molecules to 2 a subunits of an acetylcholine receptor that is composed of a2 6 subunits. The complete structure of several of the sea snake neurotoxins have been worked out. Through chemical modification studies the invariant tryptophan and tyrosine residues of post-synaptic neurotoxins were shown to be of a critical nature to the toxicity function of the molecule. Lysine and arginine are also believed to be important. Other marine vertebrate venoms are not well known. 

Sodium periodate also may affect tryptophan residues in some proteins. The oxidation of tryptophan can result in activity losses if the amino acid is an essential component of the active site. For instance, avidin and streptavidin may be severely inactivated by treatment with periodate, since tryptophan is important in forming the biotin-binding pocket. In addition, many other amino acid residues are susceptible to oxidation by periodate (Chapter 1, Section 1.1). Limiting the time of oxidation is important to restricting oxidation to diol groups while not affecting other protein structures. 

Most of the proteins on which fragment folding studies have been carried out are extracellular. Of the nine discussed in this article, only tryptophan synthetase and /3-galactosidase are not secreted. Many secreted proteins are synthesized with 20 or so additional amino acid residues at the N-terminus of the peptide chain (Blobel... 

The characteristics that discourage the use of RPLC for preparative isolation of bioactive proteins favor its use as an analytical tool for studying protein conformation. Chromatographic profiles can provide information on conformational stability of a protein and the kinetics of folding and unfolding processes. Information about solvent exposure of certain amino acid residues (e.g., tryptophan) as a function of the folding state can be obtained by on-line spectral analysis using diode array UV-vis detection or fluorescence detection. 

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