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M Liakopoulou-Kyriakides

Publications and source records attributed to M Liakopoulou-Kyriakides.

17 recordsLinked to original sources
PubMed2006

Comparative study of Cd(II) and Cr(VI) biosorption on Staphylococcus xylosus and Pseudomonas sp. in single and binary mixtures.

Biosorption of Cd(II) and Cr(VI) ions in single solutions using Staphylococcus xylosus and Pseudomonas sp., and their selectivity in binary mixtures was investigated. Langmuir and Freundlich models were applied to describe metal biosorption and the influence of pH, biomass concentration and contact time was determined. Maximum uptake capacity of cadmium was estimated to 250 and 278 mg g(-1), whereas that of chromium to 143 and 95 mg g(-1) for S. xylosus and Pseudomonas sp., respectively. In binary mixtures with Cd(II) ions as the dominant species, there is a profound selectivity for cadmium biosorption, reaching 96% and 89% for Pseudomonas sp. and S. xylosus, respectively, at 10 mg l(-1) Cd(II) and 5 mg l(-1) Cr(VI). Interesting, when chromium (VI) ions are the dominant species, there is selectivity towards chromium around 92% with S. xylosus only.

Cadmium↗
PubMed2002

Synthesis and cytogenetic effects of aminoquinone derivatives with a di- and a tripeptide.

Quinones are of significant interest due to their important role in specific cellular functions. Quinoproteins are a big class of oxyreductive agents occurring in bacteria and other organisms. In this investigation derivatives of 2-amino-1,4-benzoquinone, 2-amino-1,4-naphthoquinone and 2-amino-5,8-dihydroxy-1,4-naphthoquinone with a di- and a tripeptide were prepared for first time. The effect of the synthesized compounds on sister chomatid exchange (SCE) rates and human lymphocyte proliferation kinetics on a molar basis was studied. Among these coupled products the most effective in inducing SCEs and depressing proliferation rate indices is the coupling product of 2-amino-1,4-naphthoquinone with the tripeptide GHK (10). Next in order of magnitude in inducing cytogenetic effects is 2-amino-1,4-naphthoquinone (2) and its coupling products with glycine and serine (4 and 5), while the rest displayed marginal activity.

Benzoquinones↗
PubMed1999

Spectral analysis of a series of partially protected and deprotected tetrapeptides, analogues of AS-I phytotoxin.

A series of six tetrapeptides, analogues of AS-I phytotoxin, pathogenic to sunflower, have been synthesized either in solution and/or by solid phase methods and have been tested for phytotoxic activity in various plants and cytotoxic activity in three cancer cell lines. These peptides were identified as model compounds by fast atom bombardment (FAB), plasma desorption (PD), electrospray ionization (ESI) mass spectrometry and by 1H, 1H-1H, 13C and 1H-13C NMR. The data presented show that in protected tetrapeptides the molecular ion was easily identified whereas some difficulties appeared with the fully deprotected peptides. NMR spectra are given.

Magnetic Resonance Spectroscopy↗
PubMed1999

Cu(III)-polypeptide complexes exhibiting SOD-like activity.

The SOD-like activity of Cu(III)-complexes with polypeptides poly-L-lysine and poly-L-glutamic acid respectively was investigated. The Cu(II)-polypeptide complexes were first oxidized by K2IrCl6 to give the corresponding Cu(III)-compounds. The oxidation of Cu(II) and the corresponding Cu(II)/Cu(III) potential was evaluated by cyclic voltammetry (c.v.), UV-Vis and EPR spectroscopic (r.t.) experiments. Spin trapping EPR spectra were also conducted to confirm the formation of the superoxide radical. The SOD-like activity of each Cu(III)-complex was proved using the nitro blue tetrazolium (NBT) method slightly modified.

Copper↗
PubMed1999

Xanthan gum production by Xanthomonas campestris w.t. fermentation from chestnut extract.

Xanthomonas campestris w.t. was used for production of xanthan gum in fermentations with chestnut flour for the first time. Fermentations were carried out with either chestnut flour or its soluble sugars (33.5%) and starch (53.6%), respectively, at 28 degrees C and 200 rpm at initial pH 7.0 in flasks. The effect of agitation rate (at 200, 400, and 600 rpm) on xanthan gum production was also studied in a 2-L batch reactor. It was found that xanthan production reaches a maximum value of 3.3 g/100 mL at 600 rpm and 28 degrees C at 45 h.

Journal Article↗
PubMed1998

Antiproliferative activity of synthetic tetrapeptides, analogs of AS-I phytotoxin, towards cancer cell lines.

The in vitro chemosensitivity of three cancer cell lines [HT29 (colon), HeLa (cervical) and T47D (breast)] to eight synthetic tetrapeptides, analogs of AS-I toxin, with phytotoxic effect on a series of plants was studied. Mouse fibroblast L929 cell line was also tested for chemosensitivity to these peptides. All cell lines were especially sensitive to Cys-Val-Gly-Glu tetrapeptide with IC50 values of 0.18, 0.3 and 0.63 mM for HT29, HeLa and T47D cells, respectively, whereas the IC50 value for the L929 cells was higher than 1 mM. Antiproliferative activity was also observed with peptides Tyr-Val-Gly-Glu and His-Val-Gly-Glu with IC50 values higher than those obtained for Cys-Val-Gly-Glu. For the rest of the peptides tested the IC50 values were found close to or higher than 3 mM.

Animals↗
PubMed1992

A low molecular weight peptide from Allium porum with inhibitory activity on platelet aggregation in vitro.

A peptide factor was isolated from Allium porum with strong inhibitory activity on platelet aggregation induced by collagen or ADP. The peptide was isolated by a series of chromatographic techniques and purified to homogeneity by HPLC on RP C8 column. Its molecular weight, as it was estimated by plasma desorption mass spectrometry, is 1052 Da. Amino acid analysis showed the presence of Phe, Asp, Ser, Thr, Arg and Pro.

Allium↗
PubMed1992

Effect of X-Asp (or Asn)-Phe-Nh2 (where X; H, Met) peptides on human platelet aggregation in vitro.

A series of di- and tripeptides containing aspartic or asparagine as N-terminal or intermediate amino acid were synthesized and tested for their effect on human platelet aggregation in vitro. It was found that only Met-Asp(or Asn)-Phe-NH2 inhibited platelet aggregation induced by collagen, ADP or adrenaline. Asn-Phe-NH2 and to a small extent Asp-Phe-NH2 presented strong aggregatory activity at low concentrations (at 0.5 mM or lower than this). All the other peptides tested, did not show any effect on platelet aggregation even at the concentration of 10 mM.

Amino Acid Sequence↗
PubMed1990

Effect of leu-(Asp, Asn, Glu, Gln) dipeptides on platelet aggregation in vitro.

A series of Leu-(Asp, Asn, Glu, Gln) dipeptides were synthesized and tested for their effect on human platelet aggregation in vitro induced by collagen, ADP, or adrenaline. It was found that only Leu-Asp-NH2 and Leu-Asn-NH2 inhibit rather strongly platelet aggregation, whereas a small inhibition was observed with Leu-Glu-NH2 and Leu-Gln-NH2, respectively.

Adenosine Diphosphate↗
PubMed1990

Characterization of the platelet aggregation inducer and inhibitor isolated from Crocus sativus.

Bulbs of Crocus sativus variety Cartwrightianus were found to contain both a platelet aggregation inducer and inhibitor. The aggregating factor has a Mr of 42 kDa estimated by a Sephadex G75 column and SDS-polyacrylamide slab gel electrophoresis. It was found to lack enzymatic activity such as proteinase, esterase and acid or alkaline phosphatase. The inhibitory factor was also purified to homogeneity by different chromatographic techniques and shows a Mr of 27 kDa as it was estimated by Biogel P30 column and SDS-polyacrylamide slab gel electrophoresis. It was found to possess strong proteinase activity.

Acid Phosphatase↗
PubMed1990

Inhibition of angiotensin converting enzyme by L-alanyl-4 or 5-substituted-L-prolines and their N alpha-phosphoryl-derivatives.

A series of L-alanyl-4 or 5-substituted L-prolines, such as L-alanyl-L-thiazolidine-4-carboxylic acid, L-alanyl-5-oxo-L-proline, L-alanyl-trans-4-hydroxy-L-proline and L-alanyl-cis-4-hydroxy-L-proline as well as their corresponding N alpha-phosphoryl derivatives, were synthesized and studied for inhibition against angiotensin converting enzyme. Furanacryloyl-phenylalanyl-glycyl-glycine was used as substrate in 50 mM Tris hydrochloride buffer at pH 7.5 containing 1 microM zinc acetate. N alpha-Phosphoryl-L-alanyl-L-thiazolidine-4-carboxylic acid and N alpha-phosphoryl-L-alanyl-trans-4-hydroxy-L-proline competitively inhibit angiotensin converting enzyme with Ki values of 68 microM and 89.3 microM, respectively. Smaller inhibition against angiotensin converting enzyme was obtained with the rest of compounds studied here.

Alanine↗
PubMed1982

s-Cis...and s-trans isomerism in acylproline analogs. Models for conformationally locked proline peptides.

N-Acetyl-2,3-dehydroproline, N-acetyl-5-oxo-L-proline, N-acrylyl-L-proline, N-acetyl-L-azetidine-2-carboxylic acid and N-acetyl-D,L-pipecolic acid have been examined in 2H2O by 1H and 13Cn.m.r. for the purpose of finding s-cis or s-trans locked acylprolines. Conformationally locked acylprolines could be incorporated into proline-containing peptide hormones such as angiotensin and thyroliberin in order to determine the rotational state of the peptide bond to proline in the hormone receptor complex. The populations of trans and cis rotational isomers were determined as a function of p2H in order to assign the trans and cis isomers and to compare the populations in all the acylprolines at neutral p2H, where the cis isomer is normally present. Proton spectra were also recorded at from 7 degrees to 75 degrees in order to qualitatively determine the exchange rate between the isomers. The majority of these analogs exhibit a cis-trans isomerization similar to that of N-acetyl-L-proline in the ratio of trans to cis rotational isomer found at neutral p2H (about 1:1), the temperature dependence of the population ratio (none), and the coalescence temperature for proton resonances (greater than 75 degrees). However, N-acetyl-5-oxo-L-proline was found to be greater than 98% s-trans at neutral pH, compared to 50% s-trans in N-acetyl-L-proline, and therefore a good candidate for synthesis of an s-trans locked peptide hormone. N-Acetyl-2,3-dehydroproline rapidly exchanges between s-cis and s-trans in contrast to all other proline analogs examined and exhibits coalescence of the beta-proton cis and trans resonances at 45 degrees. Titration with the shift reagent Pr+++ was employed to confirm the assignments of the cis and trans methyl resonances of all of the N-acetyl compounds except N-acetyl-5-oxo-L-proline.

Magnetic Resonance Spectroscopy↗
PubMed1982

The rate of s-cis/s-trans isomerization in angiotensin II is at least 70-fold greater than in His-Pro and is not rate limiting in receptor binding.

The dipeptide L-histidyl-L-proline interconverts between the s-cis and s-trans rotational isomers of the amide bond with an average rate constant of 2.0 ks-1 at 22.5 degrees. This rate is independent of pH throughout the pH range 5.5-8.5 as determined by pH jump from low pH with potentiometric recording of the slow approach to equilibrium pH, and by integration of the histidine C-2 and C-4 proton n.m.r. resonances as a function of time following pD jump from low pD. From the temperature dependence of the n.m.r. experiments this interconversion has an Arrhenius activation energy of 20 kcal X mol-1 and a free energy of activation of 21 kcal X mol-1, similar to other simple acyl- and aminoacylprolines. The octapeptide angiotensin II containing L-histidyl-L-proline at position 6-7 interconverts at least 70-fold faster than the free dipeptide. This rate is too fast to be rate limiting in the binding of angiotensin II to its receptor in rat adrenal cortex.

Angiotensin II↗
PubMed1979

s-Cis and s-trans isomerism of the His-Pro peptide bond in angiotensin and thyroliberin analogues.

The dipeptide His-Pro isomerizes from all-s-trans to partly s-cis when titrated in D2O from acidic to neutral pD as observed by 13C and 1H nuclear magnetic resonance of the proline side chain. This isomerization is reported by the His C-2 and C-4 protons and carbons which show distinct, well-resolved resonances for each isomer. The influence of the His-Pro peptide bond rotational state on the histidine protons far removed from the bond has not been previously observed in model compounds or peptides. The peptides thyroliberin (TRH), [3-MeHis2]-TRH, and [3-MeHis6]-, [Sar1,Al8]-, and Nalpha-acetylangiotensin II were found to similarly isomerize from all-s-trans to partly s-cis as reported by their His C-2 and C-4 proton resonances. The His C-2 and C-4 protons in the peptides [1,3-diMeHis2]-TRH and [1-MeHis6]-, and [homoHis6]-angiotensin do not report this isomerization. Angiotensin II has previously been found to exhibit the same isomerization. The reporting of the s-trans to s-cis isomerization by the His C-2 proton appears to be correlated with the known potencies of the five angiotensin peptides in rat uterine strips and of the three TRH peptides by radioimmunoassay of released thyrotropin.

Angiotensin II↗
PubMedDate not supplied

Hyperalkaline and thermostable phosphatase in Thermus thermophilus.

The phosphatases existing in the extreme thermophilic bacterium Thermus thermophilus have been studied. Utilizing ion exchange, hydrophobic, pseudoaffinity, and affinity chromatography, a number of distinct phosphatase activities were identified. At least four phosphatases, with optimum pH ranging between 5.0 and 11.5, were assayed with p-nitrophenylphosphate, and two with optimum pH between 7.0 and 11.0, with 32P-casein as substrate. The authors have focused on the hyperalkaline phosphatase and have tried to purify and characterize it. This hyperalkaline phosphatase reaches a maximal level at the stationary phase of the growth, and is co-purified with alkaline phosphatase with optimum pH of 10.2. The enzymes present a relative mol wt of 65 and 58 kDa, respectively, as judged by SDS-PAGE and Sephadex G-150 column, and possess similar properties, indicating that they are isoforms. These enzymes barely function in the presence of tartrate, and are inhibited by EDTA, pyrophosphate, and molybdate. Among the metals tested, Hg2+ appeared as the strongest inhibitor of the hyperalkaline phosphatase. The two enzymes are thermostable and, upon treatment at 90 degrees C for 10 min, 75% of their activity remains. The physiological role and function of these phosphatases need further investigation.

Alkaline Phosphatase↗