Tyrosine-containing peptides

Peptides may also be detected by means of a fluorescence detector using the natural fluorescence of certain amino acids or by forming fluorescent derivatives. Tyrosine and tryptophan are fluorescent, and this property can be used to detect peptides that contain these amino acids. The excitation wavelength for these amino acids has been established to be between 220 and 280 nm, with the greatest sensitivity at 220 nm. In alkaline solutions the emission band is 365 nm for tryptophan and 310 nm for tyrosine. Peptides containing both these amino acids have been detected at an emission wavelength of 330 nm (94). 

Pish protein concentrate and soy protein concentrate have been used to prepare a low phenylalanine, high tyrosine peptide for use with phenylketonuria patients (150). The process includes pepsin hydrolysis at pH 1.5 ptonase hydrolysis at pH 6.5 to Hberate aromatic amino acids gel filtration on Sephadex G-15 to remove aromatic amino acids incubation with papain and ethyl esters of L-tyrosine and L-tryptophan, ie, plastein synthesis and ultrafiltration (qv). The plastein has a bland taste and odor and does not contain free amino acids. Yields of 69.3 and 60.9% from PPG and soy protein concentrate, respectively, have been attained. 

PTB domains recognize small peptides containing a phosphotyrosine, usually with the consensus sequence, NPXpY. Some PTB-containing proteins, such as Numb, are able to bind to the consensus peptide in the absence of phosphorylated tyrosine, suggesting phosphotyrosine is dispensable for the function of certain PTB domains. Hydrophobic residues N-termi-nal to the phosphotyrosine provide some specificity of target and distinction from SH2 domains. PTB domains appear to be particularly important in docking... 

By means of a procedure described above, Hanson and Fittkau (HI) isolated seventeen different peptides from normal urine. One of them, not belonging to the main peptide fraction, consisted of glutamic acid, and phenylalanine with alanine as the third not definitely established component. The remaining peptides contained five to ten different amino acid residues and some unidentified ninhydrin-positive constituents. Four amino acids, i.e., glutamic acid, aspartic acid, glycine, and alanine, were found in the majority of the peptides analyzed. Twelve peptides contained lysine and eight valine. Less frequently encountered were serine, threonine, tyrosine, leucine, phenylalanine, proline, hydroxyproline, and a-aminobutyric acid (found only in two cases). The amino acid composi-... 

Following the style of presentation used in Imperiali s paper concerning the synthesis of caged phosphopeptides the general route for synthesis of peptides containing 2-nitrophenylethyl-caged phosphoserine-threonine and tyrosine residue is presented below. 

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]. 

The observation that sulfation of N-terminally extended CCK peptides containing the as-partyl residue adjacent to tyrosine, e.g. of CCK-8 or CCK-10, with pyridine/S03 leads to partial sulfonation of the aromatic ring is surprising. It suggests involvement of the proximal carboxylate in the side reaction.1911... 

The tyrosine protein sulfotransferase preparations from Golgi-enriched membranes have been used for sulfation of synthetic mono- and multiple-tyrosine peptides related to known sulfation sites in proteins and peptides at analytical levels to establish the enzyme specificities.1f11-13] Preparative sulfations have not been carried out to date. A novel type of arylsulfotransferase produced by Eubacterium A-44 which is part of the human intestinal flora, has recently been discovered.1"1911111 This enzyme catalyzes the transfer of a sulfate group from phenolic sulfate, but not from 3 -phosphadenosine-5 -phosphasulfate, to other phenolic compounds. Using 4-nitrophenylsulfate as a donor substrate and tyrosine-containing peptides and proteins as acceptor substrates it catalyzes the specific sulfation of the tyrosine residues.11111-112 While this enzyme very efficiently sulfates tyrosine derivatives, the... 

A large number of fluorescence decay measurements have been performed with proteins.127 Studies on the fluorescence decay of tyrosine and tryptophan and their derivatives, and on biologically active peptides containing intrinsic or extrinsic fluorophores have also been carried out and a few illustrative examples will be reviewed here. 

Some fluorescent derivatives are specific to certain functional groups. For example, peptides containing tyrosine may be detected by adding a —CHO group to the tyrosine of the peptide by formylation with chloroform in an alkaline medium, followed by reaction with 1,2-diamino-4,5-dimethoxybenzene. The derivatives thus formed are fluorescent and can be detected at an excitation wavelength of 350 nm and an emission wavelength of 425 nm (95). 

Peptides are commonly detected by absorbance at 200-220 nm. However, most of the compounds present in wine may interfere in the ultraviolet detection of peptides when low wavelengths are used. Thus, for the analysis of these compounds it is useful to apply sensitive and selective detection methods. To this end, it is possible to form derivates of the peptides that can be detected at higher and more specific wavelengths. Detection by fluorescence can also be used to detect peptides containing fluorescence amino acids (tyrosine and tryptophan). For peptides without this property, the formation of derivates with derivatizing agents have been proved to be very useful (Moreno-Arribas et al. 1998a). 

Identification of new biomarkers of OP exposure may also lead to an understanding of why some people are intoxicated by low doses of OP that have no effect on the majority of the population. The new motif for OP binding to tyrosine may lead to new antidotes for OP poisoning for example, peptides containing several tyrosines and several arginines may be effective OP scavengers. 

Zinc arsanilazocarboxypeptidase, the product of coupling crystalline carboxypeptidase with diazotized arsanilic acid, contains one arsanilazo-tyrosyl residue per molecule. No other residues are modified. Approximately 95% of the azotyrosine can be accounted for by the isolation of a peptide containing the label on tyrosine-248 (54). 

In a histidine peptide containing no tryptophan and no tyrosine NBS may be used to advantage for the cleavage of the peptide bond next to... 

A general route to peptides containing l-(2-nitrophenyl)ethyl-caged phos-phoserine (95), -threonine (96), and -tyrosine (97) has been developed. The... 

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