Amino acid pyridoxyl esters in peptide synthesis

Pyridoxyl residue was suggested to be used as a multifunctional protective and modifying group in peptide synthesis. The modification was carried out by introducing the pyridoxyl residue in free or partially protected peptides or by the addition of amino acid pyridoxyl esters by the methods of conventional peptide synthesis without the removal of the pyridoxyl group at the terminal stages of the synthesis (the second approach is more convenient). Pyridoxyl residue was also used as a spacer in solid phase peptide synthesis. It was attached to the polymer by the alkylation of the hydroxyl groups or of the pyridine ring of the pyridoxyl derivatives with the chloromethylated styrene-divinylbenzene copolymer (the standard Merrifield resin). Potentials for the use of pyridoxyl derivatives in the synthesis of linear, multiplet, and cyclic peptides are discussed.     

Amino acid and peptide absorption from the gastrointestinal tract

Dietary proteins are digested and amino acids from these are utilized by animals to meet body needs for maintenance and production. The form in which these amino acids are absorbed and how they may be transported in the blood seem less certain than once thought. Free amino acids are absorbed and transported in the plasma as well as possibly in the blood cells. These two pools may serve unique functions and therefore deserve individual attention. Peptides are absorbed by the enterocytes. Amino acids in the peptide form appear to be absorbed more readily than free amino acids. The question of whether these peptides are hydrolyzed in the cytosol of the enterocyte or whether they can pass intact into the circulation needs more attention. Evidence suggests that the portal appearance of peptides ranges from negligible contributions to as much as 70% of the amino acids appearing in plasma.     

Amino acid requirement for the high affinity binding of a selected arginine-rich peptide with the HIV Rev-response element RNA.

The arginine-rich motif is a class of short arginine-rich peptides that bind to specific RNA structures that has been found to be a versatile framework for the design and selection of RNA-binding peptides. We previously identified novel peptides that bind to the Rev-response element (RRE) RNA of the HIV from an arginine-rich polypeptide library (ARPL) consisting of a polyarginine (15 mer) randomized at the N-terminal 10 positions. The selected peptides bound more strongly to the RRE than the natural binding partner, Rev, and contained glutamine residues that were assumed to be important for recognition of the G-A base pair. In addition, the peptides were predicted to bind to the RRE in an alpha-helical conformation. In this study, in order to understand the mechanism of the interaction between the RRE and the putative alpha-helical glutamine-containing peptides, the amino acid requirements for high affinity binding were analyzed by a combinatorial approach using a bacterial system for detecting RNA-peptide interactions. A consensus peptide, the DLA peptide, was elucidated, which consists of a single glutamine residue within a polyarginine context with the glutamine residue flanked at specific positions by three nonarginine residues, two of which appear to be important for alpha-helix stabilization. In addition, the DLA peptide was found to bind extremely tightly to the RRE with an affinity 50-fold higher than that of the Rev peptide as determined by a gel shift assay. A working model for the interaction of the DLA peptide to the RRE is proposed, which should aid in the development of peptide-based drugs that inhibit HIV replication, as well as in our understanding of polypeptide-RNA interactions. Copyright (c) 2008 European Peptide Society and John Wiley & Sons, Ltd.     

Amino acid chalcogen analogues as tools in peptide and protein research

The chalcogen elements oxygen, sulfur, and selenium are essential constituents of side chain functions of natural amino acids. Conversely, no structural and biological function has been discovered so far for the heavier and more metallic tellurium element. In the methionine series, only the sulfur‐containing methionine is a proteinogenic amino acid, while selenomethionine and telluromethionine are natural amino acids that are incorporated into proteins most probably because of the tolerance of the methionyl‐tRNA synthetase; so far, methoxinine the oxygen analogue has not been discovered in natural compounds. Similarly, the chalcogen analogues of tryptophan and phenylalanine in which the benzene ring has been replaced by the largely isosteric thiophene, selenophene, and more recently, even tellurophene are fully synthetic mimics that are incorporated with more or less efficiency into proteins via the related tryptophanyl‐ and phenylalanyl‐tRNA synthetases, respectively. In the serine/cysteine series, also selenocysteine is a proteinogenic amino acid that is inserted into proteins by a special translation mechanism, while the tellurocysteine is again most probably incorporated into proteins by the tolerance of the cysteinyl‐tRNA synthetase. For research purposes, all of these natural and synthetic chalcogen amino acids have been extensively applied in peptide and protein research to exploit their different physicochemical properties for modulating structural and functional properties in synthetic peptides and rDNA expressed proteins as discussed in the following review.     

Amino acid and peptide ratio in protein hydrolysates for parenteral feeding

Using the method of amino acid analysis and routine methods of protein biochemistry, the ratio of amino acids and peptides in acid and enzyme protein hydrolyzates was determined. Depending on the production procedure, the hydrolyzates under study contained various amounts of free amino acids and peptides in which the number of amino acid residues varied from 2 to 7. Additional hydrolysis of these preparations by leucine aminopeptidase led to a decrease in the peptide content and to an increase in the amino acid content. This may have a beneficial effect on the quality of protein hydrolyzates.     

Amino acid sequence and relative biological activity of eel atrial natriuretic peptide

A peptide exhibiting vasodepressor and natriuretic activities in rats was isolated from eel atria, and its primary structure was determined as H-Ser-Lys-Ser-Ser-Ser-Pro-Cys-Phe-Gly-Gly-Lys-Leu-Asp-Arg-Ile-Gly-Ser-Tyr-Ser- Gly-Leu-Gly-Cys-Asn-Ser-Arg-Lys-OH. This peptide, termed eel atrial natriuretic peptide (ANP), has sequence homology of 59% to mammalian (human or rat) ANP, 52% to fowl ANP, and 46% to frog ANP. When the biological activity of synthetic eel ANP was compared with that of human ANP, the eel peptide was 110 times more potent for the vasodepressor activity in eels, nearly equipotent for the vasodepressor activity in quails, and 20 times less potent for the vasodepressor and natriuretic activity in rats.     

Amino acid activation and polymerization at modular multienzymes in nonribosomal peptide biosynthesis

Summary The biosynthesis of microbial bioactive peptides is accomplished nonribosomally by large multifunctional enzymes consisting of linearly arranged building blocks of 1,000–1,500 amino acid residues. Each of these units acts as an independent enzyme which catalyzes the selection, activation, and in some cases modification (epimerization, N-methylation) of its cognate amino acid, as well as the elongation of the peptide product. The specific linkage of amino acid activating modules upon such polyenzymes defines the sequence of the peptide product. A series of functional domains could be identified upon an amino acid activating module which are involved in the sequential reactions in nonribosomal peptide biosynthesis.Abbrevations aaRS aminoacyl tRNA synthetase - GS1 gramicidin S synthetase 1 (phenylalanine racemase) - GS2 gramicidin S synthetase 2 - TY1 and 2 tyrocidine synthetase 1 and 2 - ACV [-(l--aminoadipyl)-l-cysteinyl-d-valine] - FITC fluorescein 5-isothiocyanate - FAB-, ESI-MS fast atom bombardment-, electrospray ionization-mass spectrometry - Pan 4-phosphopantetheine - NMR nuclear magnetic resonance - ACP acyl carrier protein - SAM S-adenosyl-l-methionine - CM carboxy-methyl - NES Nethylsuccinimido     

Amino acid composition and biological action of a peptide bioregulator from bovine k-casein

Peptide material has been first isolated from k-casein pepsin hydrolysate. Its subcutaneous injection to hungry animals induced high amplitude (250-350 mV) and high frequency (16-20 Hz) oscillations of electrical potentials usually observed in food satiety and cholecystokinin administration. The peptide reduced respiratory and to a lesser extent heart rate. Its effect is temporary eliminated by naloxone. According to an aminogram, the peptide is a fragment of para-k-casein. A neurotropic peptide effect is connected with satiety regulation and milk consumption in the postnatal period.     

Amino acid sequence of a specific antigenic peptide of protein B23

A specific antigenic peptide was obtained from protein B23 (Mr/pI = 37,000/5.1) after 30 min of digestion with staphylococcal V8 protease (10 micrograms/ml/mg protein B23). The antigenic peptide was purified by DEAE-cellulose chromatography and high pressure liquid chromatography on a reverse-phase C18 column. The antigenic peptide contains 14.7 and 18.7 mol% of glutamic acid and lysine, respectively. Amino acid sequence analysis showed that the peptide has 68 amino acids and is located on the carboxyl-terminal sequence of protein B23. The sequence is Ser-Phe-Lys-Lys-Gln-Glu-Lys-Thr-Pro-Lys-Thr-Pro- Lys-Gly-Pro-Ser-Ser-Val-Glu-Asp-Ile-Lys-Ala-Lys-Met-Gln-Ala-Ser-Ile-Glu- Lys-Gly- Gly-Ser-Leu-Pro-Lys-Val-Glu-Ala-Lys-Phe-Ile-Asn-Tyr-Val-Lys-Asn-Cys-Phe- Arg-Met- Thr-Asp-Gln-Glu-Ala-Ile-Gln-Asp-Leu-Trp-Gln-Trp-Arg-Lys-Ser-Leu-Cooh. Extensive digestion of the antigenic peptide with V8 protease, trypsin, or chymotrypsin results in loss of the antigenic activity. Three cloned cDNAs (hpB1, hpB2, and hpB7) which code for the 82 amino acids at the COOH terminus of protein B23 and the 3' non-translating sequence were identified and characterized. All three clones have identical nucleotide sequences coding for the antigenic portion of the protein (68 amino acids at the COOH terminus), the stop codon, and the 3' non-translated region. However, mutation of 6 nucleotide bases of one clone (hpB2) caused changes in 4 amino acids in the sequence just preceding the immunoreactive region. The result suggests the presence of at least 2 immunologically similar but distinct proteins which are both recognized by the anti-B23 antibody.