PubMed Health⌕ Search

Biomedical subjects

E Esmans

Publications and source records attributed to E Esmans.

14 recordsLinked to original sources
PubMed2005

Cobalamin as an analytical tool for analysis of oxirane metabolites of 1,3-butadiene: development and validation of the method.

The reduced form of vitamin B12 [cob(I)alamin] is known to be a supernucleophile, with the ability to react 10(5) times faster than standard nucleophiles. Procedures have been developed where cob(I)alamin is used as an analytical tool for the trapping of electrophilically reactive compounds. In the present work, a sensitive and accurate method for determination of reactive metabolites produced in vitro has been developed and validated. Diepoxybutane (DEB), a metabolite of 1,3-butadiene, was used as a model compound. The intermediate precursor 1,2-epoxybutene (EB) was incubated in a mouse liver S9 metabolic system and the formation of DEB was studied. Samples were taken at different times from the incubation mixture and added to the cob(I)alamin. The alkyl-cobalamins (alkyl-Cbl) formed were directly analysed by a miniaturized LC-MS/MS method and column switching. The assay was linear over the concentration range of 1.5-500 microM with acceptable precision and accuracy.

Animals↗
PubMed2005

Sensitive and specific quantification of the anticancer agent ZD1839 (Gefitinib) in plasma by on-column focusing capillary liquid chromatography-tandem mass spectrometry.

The development of an on-column focusing gradient capillary LC method coupled to tandem mass spectrometry (quadrupole-linear ion trap) for the quantitative determination of the anticancer agent ZD1839 (Gefitinib, Iressa) in blood plasma is described. Plasma samples (0.2 ml) were extracted with methyl tert-butyl ether. The analytes of interest, ZD1839 and the internal standard [(2)H8]ZD1839 (ZD1839-d8) were eluted on a 50 mm x 1 mm, 5 microm particle size, capillary ODS Hypersil column using an aqueous ammonium acetate gradient at 40 microl/min. Mass spectrometric detection was performed by a Q-Trap tandem mass spectrometer with electrospray positive ionisation, and monitored in the multiple reaction monitoring transitions 447 >128 and 455 >136, respectively. The limit of quantification of ZD18395 was 0.1 ng/ml. The method proved to be robust, allowing quantification of ZD1839 with sufficient precision, accuracy and sensitivity.

Antineoplastic Agents↗
PubMed1998

Structural, functional, and genetic characterization of Gastrophilus hemoglobin.

Hemoglobin of Gastrophilus intestinalis (Insecta, Diptera), was purified and characterized. At least two isoforms have been identified by isoelectrofocusing, mass spectrometry, and genomic Southern blotting. Functional studies show a high oxygen affinity due to a low ligand dissociation rate (koff = 2.4 s-1) and a relatively high autoxidation rate (t1/2 = 1.6/h). The globins were separated under denaturing conditions, and the sequence of Hb1 (Mr = 17,965 +/- 2) was determined at the protein and DNA level. The open reading frame codes for a polypeptide of 150 amino acids. Although the globin is distantly related to globins from other species, it has a low penalty score against globin templates. Freshly isolated hemoglobin was crystallized from polyethylene glycol. Crystals contain two hemoglobin molecules per asymmetric unit. Solution of the three-dimensional structure by molecular replacement could not be achieved, possibly due to the presence of three protein isoforms in the crystals. In order to determine its three-dimensional structure, G. intestinalis Hb1 was overexpressed in Escherichia coli, resulting in a fully functional molecule as confirmed by ligand binding affinity. The globin gene contains two introns at positions D7.0 and G7.0. The D7.0 intron is unprecedented, suggesting that globin gene evolution is much more complex than originally thought.

Amino Acid Sequence↗
PubMed1997

Mass spectrometric identification of phosphorylated vasostatin II, a chromogranin A-derived protein fragment (1-113).

Vasostatin II, an N-terminal chromogranin A-derived protein (CGA1-113), was purified from bovine chromaffin granule lysate and characterized by electrospray mass spectrometry (ES/MS) as being partially phosphorylated. The phosphorylation site was determined to be at the Ser81 position by mass spectrometric peptide mapping and tandem mass spectrometric analysis. This phosphorylation site is close to the processing site (...QKK78HSS(p)81...) yielding vasostatin I, an N-terminal CGA-derived peptide comprising residues 1-76, suggesting that phosphorylation at Ser81 is involved in the formation of vasostatin I in chromaffin cells.

Alkaline Phosphatase↗
PubMed1996

Characterization of unstable intermediates and oxidized products formed during cyanogen bromide cleavage of peptides and proteins by electrospray mass spectrometry.

Products formed during cyanogen bromide (CNBr) digestion of alpha-endorphin, beta-endorphin, and horse heart myoglobin are examined using reversed-phase high-performance liquid chromatography and electrospray mass spectrometry. It is demonstrated that unstable intermediate reaction products may be formed, as well as oxidized products when the CNBr reaction is performed in 0.1% TFA in water/acetonitrile (6:4 v/v) and that, under other conditions commonly employed for the CNBr cleavage reaction, unstable intermediate products are also generated. The formation of the expected cleavage products is found to be improved by adjusting the hydrolysis conditions. The structure of the intermediate formed from alpha-endorphin is examined using electrospray mass spectrometry in combination with low-energy collision-induced dissociation and tandem mass spectrometry and is shown to have a cyclic hydrated homoserine iminolactone part. The results obtained in this study explain the formation of partially cleaved proteins in the case of Met-Thr-containing sequences, which likely have a cyclic hydrated homoserine iminolactone part instead of the putative homoserine residue.

Amino Acid Sequence↗
PubMed1991

Comparison of the isolation of adducts of 2'-deoxycytidine and 2'-deoxyguanosine with phenylglycidyl ether by high-performance liquid chromatography on a reversed-phase column and a polystyrene-divinylbenzene column.

2'-Deoxycitidine (dCyd) and 2'-deoxyguanosine (dGuo) were subjected to reaction with phenylglycidyl ether (PGE) in methanol in order to study the formation of the corresponding 2'-deoxynucleoside adducts. Separation methods were developed on analytical and semi-preparative scales using high-performance liquid chromatography with photodiode-array detection on a reversed-phase column and on a polystyrene-divinylbenzene column. The use of the latter column was prompted by decomposition of the preparatively isolated dGuo-PGE adducts on the reversed-phase column. The use of a polystyrene-divinylbenzene column solved this problem and also revealed the presence of one more peak in both the dCyd- and dGuo-PGE reaction mixtures. The adducts of dCyd and dGuo were isolated on preparative reversed-phase and polystyrene-divinylbenzene columns and characterized by UV, fast atom bombardment mass and 360 MHz 1H NMR spectrometry. The adducts of dCyd were the diastereomers of N-3-(2-hydroxy-3-phenoxypropyl)-2'-deoxycytidine and N4-(2-hydroxy-3-phenoxypropyl)-2'-deoxycytidine whereas those of dGuo were the two diastereomers of N-7-(2-hydroxy-3-phenoxypropyl)-2'-deoxyguanosine and a third peak which appeared to be mainly N2-(2-hydroxy-3-phenoxypropyl)-2'-deoxyguanosine.

Chromatography, High Pressure Liquid↗
PubMed1989

On the use of laser microprobe mass spectrometry for the analysis of organic biomolecules.

Laser microprobe mass spectrometry has been applied to a variety of organic polyfunctional molecules, covering a wide range of polarity and mass spectrometric behaviour. The technique apparently combines desorption under relatively soft conditions with extensive fragmentation and hence allows much structural information from intactly released thermolabiles to be obtained. The mass spectra appear unfamiliar in comparison to conventional techniques. Interpretation is attempted in a purely empirical way by means of the evidence from our database and tentative hypotheses to rationalize the desorption and ionization by laser microbeam irradiation of organic solids. Selected examples are presented to illustrate the potential and limitations of the method in the field of biomolecules, such as pyridoxine and pyridoxal phosphate, nucleosides, nucleotides and related analogues, drugs and the corresponding N-oxides.

Flunarizine↗
PubMed1981

Isolation and identification of 2-oxo-5-guanidinovaleric acid in urine of patients with hyperargininaemia by chromatography and gas chromatography/mass spectrometry.

An unknown guanidino-positive peak has been identified in urines of three sisters affected with hyperargininaemia. Identification was made on the basis of its similarity with the liquid and thin-layer chromatographic characteristics of enzymatically synthesized 2-oxo-5-guanidinovaleric acid. Identification was also made by combined gas chromatography-mass spectrometry of the unknown compound peak. The synthesis of enzymatically formed 2-oxo-5-guanidinovaleric acid was controlled by nuclear magnetic resonance and combined gas chromatography-mass spectrometry.

Amino Acid Metabolism, Inborn Errors↗
PubMed1979

Isolation and identification of polyprenols from bovine thyroid gland.

The presence of polyprenols in bovine thyroid was demonstrated. After preparative isolation, the structure was elucidated by chemical and spectroscopic techniques. The main polyprenol homologue has a molecular weight of 1380 corresponding to the presence of 20 isoprene units. From NMR studies it appears that 18 units have the cis configuration and that the 2 others are trans isoprene units. The dolichol content amounts to 0.2 mg/g wet weight. About 5% was found in the esterified form.

Animals↗
PubMedDate not supplied

Plant antiviral agents. III. Isolation of alkaloids from Clivia miniata Regel (Amaryllidaceae).

Lycorine (1), one of the main alkaloids of the Amaryllidaceae family, was found to be responsible for the pronounced antiviral activity of the crude extracts from the roots and leaves of Clivia miniata Regel. It was shown that the inhibitory activity of lycorine on the cytopathogenic effect caused by a DNA and several RNA viruses on VERO cells was not virucidal. Poliomyelitis virus inhibition occurred at lycorine concentrations as low as 1 microgram/ml, whereas concentrations exceeding 25 micrograms/ml were found to be cytotoxic. Clivimine (2), clivonine (3) and cliviamartine (4) were also isolated and characterized, but these alkaloids exhibited no antiviral properties.

Alkaloids↗
PubMedDate not supplied

Plant antiviral agents, VI. Isolation of antiviral phenolic glucosides from Populus cultivar Beaupre by droplet counter-current chromatography.

Bioassay-guided isolation of the 80% EtOH extract of the leaves of Populus cultivar Beaupré by means of dccc afforded four known phenolic glucosides. Salicin and salireposide were shown to be, at least partially, responsible for the antiviral activity of the extract against poliomyelitis and Semliki forest viruses.

Antiviral Agents↗
PubMedDate not supplied

Urinary modified nucleosides as tumor markers.

Extracts of urinary nucleosides have been sequentially purified and examined by mass spectrometric analysis. Seventeen modified nucleosides have been unequivocally identified and a further five provisionally identified. While several nucleosides were found only in a small number of extracts, the occurrence and levels of others were found to correlate with the tumour type and stage.

Biomarkers, Tumor↗