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C Tzougraki

Publications and source records attributed to C Tzougraki.

13 recordsLinked to original sources
PubMed2001

Synthesis and characterization of a binuclear coumarin-3-carboxylate copper(II) complex.

The copper(II) complex of coumarin-3-carboxylic acid (CcaH) has been prepared and characterized on the basis of elemental and thermal analysis, IR, Raman, EPR, UV-Vis reflectance and 1H-NMR spectra. A detail analysis of all spectra data is presented with particular emphasis on the elucidation of the coordination mode of the ligand and the structure of the complex. All data are consistent with a binuclear structure for the complex with four coumarin-3-carboxylates as bridges and one water ligand per copper ion. The significantly lower than the spin-only value magnetic moment of the complex and the EPR spectra at various temperature are indicative of a magnetic interaction between the two copper atoms.

Copper↗
PubMed2001

NMR and CD conformational studies of the C-terminal 16-peptides of Pseudomonas aeruginosa c551 and Hydrogenobacter thermophilus c552 cytochromes.

The 16-amino acid sequences of the C-terminal helices of the homologous bacterial cytochromes c551 from Pseudomonas aeruginosa and C552 from Hydrogenobacter thermophilus were synthesized and their solution structure studied. Circular dichroism and NMR experiments in aqueous solution have shown the presence of alpha-helices and 3(10)-helices. The populations of helical structures in phosphate buffer, pH 3.5, 293 K, were 21% for c551 and 20% for c552, but increased to 56.7 and 48%, respectively, in 50% aqueous 2,2,2-trifluoroethanol. An isodichroic point was observed at 203 nm in CD spectra for the helix/coil transition in mixtures of water/2,2,2-trifluoroethanol. NMR spectra in phosphate buffer show the presence of both alpha- and 3(10)-helical structures. In water/2,2,2-trifluoroethanol (50:50) alpha-helices are predominant. CD temperature-dependency studies indicate that both peptides exhibit the same cooperativity for the transition in water/2,2,2-trifluoroethanol (50:50). The experimental data show that the amino acid substitutions do not favor heat resistance of the secondary structure of the c552 C-terminal helix at the local level. Instead, they optimize nonlocal contacts of the polypeptide chain, which stabilize the tertiary structure in the native protein.

Algorithms↗
PubMed2000

Synthesis and fluorescence properties of intramolecularly quenched fluorogenic p-nitroanilides containing coumarin or quinolinone derivatives as fluorophores.

Nine model intramolecularly quenched fluorogenic substrates (IQFS) of the general structure F-Phe-NH-Np, containing coumarin or quinolinone derivatives as fluorophores (F) and the p-nitroanilide group (Np) as quencher, were synthesized. The study of the fluorescence properties of the substrates synthesized and the corresponding fluorophores showed that efficient quenching of fluorescence (>89%) was observed in all cases. The combination of 7-glutarylamido-4-methyl-coumarin (Mec-NH-Glt-OH) or 7-methoxy-4-coumaryl-acetic acid (Mca) with the p-nitroanilide group gave the best results (97.2 and 98.8% quenching, respectively). These fluorophores can be used to convert peptide p-nitroanilides into IQFS, which, retaining their chromogenic properties, may be applied in both fluorometric and colorimetric assays.

Aniline Compounds↗
PubMed1997

New fluorogenic substrates for the study of secondary specificity of prolyl oligopeptidase.

The secondary specificity of prolyl oligopeptidase (POP) has been studied by using a series of fluorogenic substrates containing the highly fluorescent 7-amino-4-methyl-2-quinolinone (AMeq) marker. The substrates were dipeptides of the general formula Z-X-Pro-NH-Meq, bearing amino acid residues with variable functional groups [Met, Lys(Boc), Lys, His, Ser, Leu, Glu(OMe), Glu, Cys(Bzl)] at the P2 position, and the tripeptide Z-Asn-Cys(Bzl)-Pro-NH-Meq. The kinetic parameters for their hydrolysis by porcine kidney POP were determined at lambda ex = 360 nm and lambda em = 430 nm. All the dipeptide substrates showed a high affinity to the enzyme and could be used for its fluorometric determination. The S2 binding subsite of POP can accommodate amino acid residues with a bulky side group, while it prefers a positively charged group (free Lys) instead of a negatively charged one (free Glu).

Fluorescent Dyes↗
PubMed1992

Inhibition of human serum oxytocinase (cystine aminopeptidase, E. C. 3.4.11.3) by GnRH peptides.

The hydrolysis of H-Cys(Bzl)-NH-Meq by human serum oxytocinase (E.C. 3.4.11.3) was inhibited non-competitively by various pyroglutamyl peptides. The most effective were the chicken GnRH II (Ki = 6 x 10(-6) mol l-1) and salmon GnRH (Ki = 12 x 10(-6) mol l-1), while the inhibitory potency of human GnRH was substantially lower (Ki = 60.0 x 10(-6) mol l-1). Variations in inhibitory potency of individual peptides reflected mostly the differences in N-terminal and C-terminal parts of the molecules.

Amino Acid Sequence↗
PubMed1990

Fluorogenic substrates for chymotrypsin with 2-quinolinone derivatives as leaving groups.

Sensitive and convenient fluorometric assays for the determination of chymotrypsin have been developed by using the substrates Glt-Leu-Phe-NH-Meq, Glt-Phe-NH-FMeq and Glt-Leu-Phe-NH-FMeq, which have been synthesized utilizing the mixed anhydride method. The amidolytic activity of chymotrypsin was measured by the release of the highly fluorescent amine 7-amino-4-methyl-2-quinolinone (AMeq) or 7-amino-4-trifluoromethyl-2-quinolinone (AFMeq). The fluorescence properties of the synthesized substrates and the new fluorescent marker AFMeq were examined. Kinetic constants, as well as the maximum sensitivity for the hydrolysis of the new substrates, were determined. All new substrates permit a rapid and sensitive determination of chymotrypsin in a continuous assay system. As little as 0.7 ng of enzyme can be detected using the substrate Glt-Leu-Phe-NH-Meq, which is the most sensitive fluorogenic substrate thus far reported.

Amino Acid Sequence↗
PubMed1987

Studies on immunoassays of peptide factors. V. Synthesis of cholecystokinin-58-[1-11]/iso-1-cytochrome c conjugate.

In previous studies on model compounds we have found that the maleimide function is sufficiently stable under the conditions of peptide synthesis to allow its incorporation at preselected positions of a peptide chain in earlier steps of the synthetic route. Taking advantage of this observation the N-terminal undecapeptide of canine cholecystokinin-58 containing at its N-terminus the maleimide group became accessible in high yields as chromatographically homogenous and analytically well characterized compound. Via the incorporated anchor group the undecapeptide was linked selectively at its N-terminus to the cysteine residue 107 of iso-1-cytochrome c to yield a well characterized conjugate of 1:1 stoichiometry for immunization experiments.

Cholecystokinin↗
PubMed1986

Fluorogenic substrates for chymotrypsin with new fluorescent markers.

Several substrates for chymotrypsin Glt-Phe-NHRx have been synthesized, where RxNH2 are the compounds 3-aminocoumarin (2), 6-aminocoumarin (3), 3-acetamido-6-aminocoumarin (4), 3-acetamido-8-aminocoumarin (5), 7-amino-4-methyl-2-quinolinone (AMQ), (6). The fluorescence properties of the new substrates and those of the corresponding free amines were examined. The compound 7-glutarylphenylalaninamido-4-methyl-2-quinolinone (Glt-Phe-AMQ), (15), provided a new suitable substrate for chymotrypsin determination. The enzymatic release of the fluorophore AMQ was measured at lambda ex = 360 nm and lambda em = 435 nm. The Km of 15 was 0.5 mM and its kcat/Km ratio was 47 M-1 s-1. By using this substrate, the detection limit of chymotrypsin was 10 ng/ml.

Chymotrypsin↗
PubMed1986

Synthesis of a potent enkephalin analog, Tyr-D-Thr-Gly-Phe-delta 3 Pro-NH2, and some of its biological activities.

The enkephalin analog, H-Tyr-D-Thr-Gly-Phe-delta 3 Pro-NH2 X HCl (VI) ([D-Thr2, delta 3 Pro5]-enkephalinamide), has been synthesized by conventional methods in solution and purified to homogeneity by reversed phase HPLC. The analog is a potent analgesic agent. For evaluation of some of its biological activity a related compound [D-Thr2, Thz5]-enkephalinamide (XI) was also synthesized in solution. Anti-diarrhea activity was evaluated in mice by the intravenous route for anti-DL-5-hydroxytryptophan (5-HTP) induced diarrhea activity. Analgesic activity was assayed by the method of Nilsen in mice using the intravenous route, and by a modified tail flick test in rats and the acetic acid writhing test in mice following subcutaneous administration. Within the constraints of the assays the two analogs are approximately equipotent. Both are less active than [D-Ala2, MePhe4, Met(0)ol]-enkephalinol (XII). Earlier receptor binding studies of compound XI indicated enhanced affinity for the mu receptor and little for the delta receptor. By comparison this may also be the case for compound VI.

Analgesics↗
PubMed1980

Synthesis of human beta-endorphin in solution using benzyl-type side chain protective groups.

A solution synthesis of human beta-endorphin (beta-EP) was carried out by condensation of protected peptide segments bearing N alpha-tert.-butyloxycarbonyl groups and benzyl-derived groups for the protection of functionalities in amino acid side chains. Five intermediate segments were assembled in a stepwise manner starting at the carboxyl terminus. Thus, the segment of sequence region (27-31) was coupled to segment (22-26) by the azide method. Segment (19-21) was incorporated into the growing chain by azide coupling, and segment (10-18) by dicyclohexylcarbodiimide coupling in the presence of 1-hydroxybenzotriazole (DDC-HOBt). Solubility problems in condensing the ensuing 22-peptide with segment (1-9) by DDC-HOBt were overcome by using a dimethylformamidephenol mixture as a solvent. Protecting group cleavage by Na in liquid NH3 was much superior to liquid HF which gave rise to many decomposition products. Homogeneous betah-EP indistinguishable from authentic material in physiochemical and biological properties, was obtained in a single preparative reversed phase liquid chromatographic step after protecting group cleavage.

Amino Acid Sequence↗
PubMed1979

Synthesis and some pharmacological properties of [Glu(OMe)4]oxytocin and [Mpr1, Glu(OMe)4]oxytocin.

[Glu(OMe)4]oxytocin (XVI) and [Mpr1, Glu(OMe)4]oxytocin (XVII) bearing a methyl ester group in place of the carboxamide group in position 4 of oxytocin were synthesized by (3 + 6) segment condensation using the S-trityl group for the protection of the cysteine side chains. Analogue XVI exhibited 10.5 U/mg in vitro uterotonic, and 42 U/mg avian vasodepressor, activity, and analogue XVII 21.4 U/mg and 82 U/mg of the respective activities. Both compounds showed no response in the rat pressor assay.

Amino Acid Sequence↗