Kinetics and mechanism of peptide synthesis in solution

The kinetics of the reaction of Boc-Xaa fluorophenyl esters (where Xaa = Ala, Val, Phe, Ser, Leu, Gly, Met, Pro, or Ile) with leucinamide was studied measuring changes in the fluorescence emission at 375 nm of the fluorophenyl chromophore accompanying the reaction. It was found that the experimental kinetic data couldn't be described by a simple scheme of the second order reaction. The measurements of the kinetic parameters of the reaction at various initial concentrations of reagents indicated that the reaction rate can be expressed as: v = kCNaCAEb, where k is the reaction rate constant, CN is the concentration of leucinamide, and LeuNH2, CAE is the concentration of fluorophenyl ester. The a and b reaction orders were close to 1/2 and 3/2 for Xaa = Ala, Val, Phe, Ser, or Leu, 1/2 and 1 for Gly, Met, or Pro, and 1 and 2 for Ile. The experimental equations for the reaction rate can theoretically be derived from a single scheme of chain reactions with various deactivation ways for active intermediates. The English version of the paper.     

Dipentafluorophenyl carbonate--a reagent for peptide synthesis

Dipentafluorophenylcarbonate, belonging to transesterifiying reagents, has been prepared and used for the synthesis of pentafluorophenyl esters of amino acids. In contrast to many other reagents of the kind, its preparation is simple, it is highly reactive and at the same time stable upon storage.     

Kinetics and Mechanism of the Peptide Synthesis in Solution

The kinetics of the reaction of Boc-Xaa fluorophenyl esters (where Xaa = Ala, Val, Phe, Ser, Leu, Gly, Met, Pro, or Ile) with leucinamide was studied in order to measure changes in fluorescence emission at 375 nm of the fluorophenyl chromophore accompanying the reaction. It was found that the experimental kinetic data could not be described by a simple scheme of the second order reaction. Measurements of the kinetic parameters of the reaction at various initial concentrations of reagents indicated that the reaction rate can be expressed as: = kC _N ^a C _AE ^b , where k is the reaction rate constant, C _N is the concentration of leucinamide, and C _AE is the concentration of fluorophenyl ester. The a and b reaction orders were close to 1/2 and 3/2 for Xaa = Ala, Val, Phe, Ser, or Leu, 1/2 and 1 for Gly, Met, or Pro, and 1 and 2 for Ile. The experimental equations for the reaction rate can theoretically be derived from a single scheme of chain reactions with various deactivation ways for active intermediates.     

Prolonged stimulation of hematopoiesis in mice with chemotactic peptide N-f-met-leu-phe-gly incorporated into liposomes

The experimental study of macrophage-activating chemotactic peptide N-f-met-leu-phe-gly (chemotaxic peptide), as well as its liposomal form, on the proliferation and migration of colony-forming precursor cells in mice was carried out. The study revealed that the subcutaneous injection of chemotaxic peptide into mice in a dose of 20 Mg led to a pronounced, but short-term increase in the proliferation of such precursor cells in the marrow: as shown by the hydroxyurea "suicide" method, a day after the injection almost 50% of hematopoietic stem cells entered the S-phase of the cellular cycle; in addition, an increase in the content of colony-forming precursor cells in the peripheral blood and the spleen was observed. The injection of chemotaxic peptide, incapsulated into liposomes, led to a considerable increase in the duration of the stimulating effect, manifested by the maintenance of a stable proliferative state of the pool of hematopoietic stem cells during 4 weeks (the term of observation). This effect could be attributed to the formation of the liposomal "depot" and the gradual liberation of chemotaxic peptide from it.     

Ca-inhibited binding of melittin with parvalbumin. A new role for parvalbumins?

It was found that pike parvalbumins pI 4.2 and 5.0 bind amphiphilic peptide melittin extracted from bee venom in an extraordinary Ca-dependent manner: in apo-state the protein forms a tight equimolar complex with melittin (Ka = 10(6) M-1 at 18 degrees C); in Ca- (and Mg-) loaded state it does not take place. Heating of the protein up to temperatures above the denaturation temperature of apo-parvalbumin does not change the stoichiometry of the complex but increases its association constant by an order of magnitude (Ka = 1.2.10(7) M-1 at 44 degrees C). Isolated Ca-binding domain of parvalbumin, 38-108, retains the ability for Ca-inhibited binding of equimolar quantities of melittin. The possible function of parvalbumin in vivo is suggested: Ca-inhibited interactions with some intracellular components.     

Partial molar volumes of polypeptides and their constituent groups in aqueous solution over a broad temperature range

The partial molar volumes of various compounds that model protein constituent groups, such as tripeptides (Gly-X-Gly, where X = Gly, Ala, Val, Leu, Ile, Pro, Met, His, Ser), homopeptides (Glyn, n = 3,4,5), and simple organic analogues of amino acid side chains (methanol, acetamide, propanamide, acetic acid, propanoic acid, n-butanamine, n-butanamine nitrate, n-propylguanidine nitrate, 4-methylphenol), have been determined in aqueous solution with a vibrational densimeter in the temperature range of 5-85 degrees C. The partial molar volumes of amino acid side chains and the peptide unit were estimated from the data obtained. Assuming additivity of component groups, the partial molar volumes of polypeptide chains of several proteins over a broad temperature range were calculated. The partial molar volume functions of four proteins (myoglobin, cytochrome C, ribonuclease A, lysozyme) were compared with those determined experimentally for the unfolded and native forms of these proteins. It has been shown that the average deviation of the calculated functions from the experimental ones does not exceed 3% over the temperature range studied.     

Sodium and potassium binding to parvalbumins measured by means of intrinsic protein fluorescence

The binding of Na+ and K+ to whiting parvalbumin (pI 4.4) and pike parvalbumins (pI 4.2 and 5.0) results in a shift of the tryptophan fluorescence spectrum towards shorter wavelengths by 2-4 nm for the whiting protein and in a rise of the tyrosine and phenylalanine fluorescence quantum yield for the pike proteins. The effective binding constants of Na+ and K+ to parvalbumins are within the range of 10 M-1 to 100 M-1. Physiological concentrations of Na+ and K+ lower the affinity of whiting parvalbumin for Ca2+ and Mg2+ by almost an order of magnitude.     

Modeling of alpha-superhelical proteins. Selection of sequence, synthesis, and properties

An analysis of the alpha-tropomyosin primary structure suggests a periodic sequence able to form an alpha-superhelical conformation. A repeating unit (the heptapeptide monomer) was obtained by sequential synthesis in solution using pentafluorophenyl esters of the N-protected amino acids. The polyheptapeptide (Glu-Lys-Lys-Leu-Glu-Glu-Ala)n with an average molecular weight 6500 has been synthesized by polymerization of the heptamer. It is shown that the polymer product forms a stable alpha-superhelix at acidic pH in water solution.     

Synthesis of tetracontapeptide--a hypothetical evolutionary precursor of calcium-binding proteins. II. Condensation of fragments

A tetracontapeptide was obtained by condensation of synthetic fragments (see the preceding paper) with the use of pentafluorophenyl esters as well as with carbodiimide and hydroxybenzotriazole. Racemization during fragment condensation was 1-2 per cent. Deblocking of the protected tetracontapeptide was carried out by treatment with trifluoroacetic acid and hydrogen fluoride with thioanisole. The obtained peptide was purified by gel-chromatography and HPLC.