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Biomedical subjects

W Hammes

Publications and source records attributed to W Hammes.

15 recordsLinked to original sources
PubMed2000

Quantitative determination of alpha-cyclodextrin in human plasma by liquid chromatography/positive ion electrospray mass spectrometry.

A sensitive and selective method for the determination of alpha-cyclodextrin in human plasma is described using beta-cyclodextrin as an internal standard. After protein precipitation with perchloric acid, the analytes were isolated from human plasma by solid-phase extraction on Bond Elut C18 cartridges. The compounds were chromatographed on a narrow-bore aminopropyl column (125 x 2 mm i.d., 5 microm) and analyzed by electrospray ionization mass spectrometry in the positive selected-ion mode using the [M+NH4]+ ion. The lower limit of quantitation was 5 ng ml(-1) of human plasma. Linear calibration curves were obtained over the concentration range 5-1000 ng ml(-1) of human plasma. The intra- and inter-assay precisions were <18% and the accuracy was <10.5% over the entire concentration range. During the method development, the ionization efficiencies of the analytes in plasma samples originating from different sources were examined to overcome the matrix effect problems caused by co-eluting endogenous compounds. The method was successfully applied to pharmacokinetic studies in human volunteers.

Blood Chemical Analysis↗
PubMed1999

Simultaneous determination of prostaglandin E1, prostaglandin E0 and 15-keto-prostaglandin E0 in human plasma by gas chromatography/negative-ion chemical-ionization tandem mass spectrometry.

A sensitive and selective routine method for the simultaneous determination of prostaglandin E1 (PGE1), prostaglandin E0 (PGE0) and 15-keto-prostaglandin E0 (15-keto-PGE0) in human plasma is described using deuterated internal standards. The analytes were isolated from acidified human plasma by solid-phase extraction by means of Bond Elut C18 cartridges and derivatized to the pentafluorobenzyl (PFB) ester methoxime. The analytes were purified on Bond Elut Si cartridges and converted to the trimethylsilyl (TMS) ether. Quantitation was achieved by gas chromatography-negative-ion chemical-ionization tandem mass spectrometry. The precursor ion [M-PFB]- = [P]- carried more than 80% of the total ion current. Collision activated decomposition (CAD) of [P]- resulted in characteristic product ions of which the [P-2(CH3)3SiOH]- ion (PGE1) and the [P-(CH3)3SiOH]- ion (PGE0 and 15-keto-PGE0) were used for quantitation. The lower limit of quantitation (LLQ) was 2 pg/ml (PGE1 and PGE0) and 10 pg/ml (15-keto-PGE0) extracted from 2 ml of human plasma. Linear calibration curves were obtained over the concentration range 2-100 pg/ml (PGE1 and PGE0) and 10-500 pg/ml (15-keto-PGE0). In all cases, the precision and accuracy were < 17%. The present method has been applied successfully to pharmacokinetic and clinical studies in humans.

Calibration↗
PubMed1997

[Divorces, 1996].

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Adolescent↗
PubMed1995

Simultaneous determination of moexipril and moexiprilat, its active metabolite, in human plasma by gas chromatography-negative-ion chemical ionization mass spectrometry.

A sensitive and selective method for the simultaneous determination of moexipril and moexiprilat, its active metabolite, in human plasma is described using quinapril and quinaprilat as internal standards. The analytes are isolated from human plasma by means of Bond Elut C18 cartridges, methylated with diazomethane, purified by acid-base partitioning and converted to the corresponding trifluoroacetamides using trifluoroacetic anhydride. Moexipril and moexiprilat were analysed by gas chromatography-negative-ion chemical ionization mass spectrometry (GC-NICI-MS) at the fragment ions m/z 302 and m/z 288, respectively. The lower limit of quantitation both for moexipril and moexiprilat is 0.5 ng/ml of human plasma. Linear calibration curves are obtained over the concentration range 0.5-300 ng/ml of human plasma. In any case the imprecision and the inaccuracy are < 15%. The present method has been successfully applied to various pharmacokinetic studies in human subjects and patients.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1995

[Divorces, 1994].

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Adolescent↗
PubMed1995

[Divorces, 1995].

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Age Factors↗
PubMed1994

[Divorces 1992].

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Adolescent↗
PubMed1994

[Divorces, 1993].

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Adolescent↗
PubMed1990

Isolation of nucleotide activated amino acid and peptide precursors of the pseudomurein of Methanobacterium thermoautotrophicum.

The following putative precursors of the pseudomurein were isolated from trichloroacetic acid extracts of Methanobacterium thermoautotrophicum: a uridine diphosphate activated derivative of glutamic acid and the uridine diphosphate activated peptides (see text). The activated glutamic acid residue and the three activated pepetides lack the glycan components N-acetylglucosamine and N-acetyltalosaminuronic acid present in the intact pseudomurein. In this case uridine diphosphate should be directly linked to the amino group of a glutamic acid residue, which represents a new mode of amino acid and peptide activation.

Amino Acid Sequence↗
PubMed1989

Biosynthesis of pseudomurein: isolation of putative precursors from Methanobacterium thermoautotrophicum.

In aqueous trichloroacetic acid extracts of Methanobacterium thermoautotrophicum the following compounds, which are supposed to be precursors in the biosynthesis of the glycan strand of the pseudomurein, were isolated and identified: (i) a disaccharide (compound II) composed of uridine 5'-diphosphate, N-acetylglucosamine and N-acetyltalosaminuronic acid with N-acetylglucosamine at the reducing end, (ii) uridine 5'-diphospho-N-acetylglucosamine, and (iii) uridine 5'-diphospho-N-acetylgalactosamine. However, the corresponding monomeric derivative of N-acetyltalosaminuronic acid could not be detected. It is assumed that N-acetyltalosaminuronic acid may be formed from N-acetylgalactosamine by epimerisation and oxidation at the disaccharide level. These findings indicate that the biosynthetic pathways of murein and pseudomurein are quite different.

Acetylglucosamine↗
PubMed1973

Mode of action of glycine on the biosynthesis of peptidoglycan.

The mechanism of glycine action in growth inhibition was studied on eight different species of bacteria of various genera representing the four most common peptidoglycan types. To inhibit the growth of the different organisms to 80%, glycine concentrations from 0.05 to 1.33 M had to be applied. The inhibited cells showed morphological aberrations. It has been demonstrated that glycine is incorporated into the nucleotide-activated peptidoglycan precursors. The amount of incorporated glycine was equivalent to the decrease in the amount of alanine. With one exception glycine is also incorporated into the peptidoglycan. Studies on the primary structure of both the peptidoglycan precursors and the corresponding peptidoglycan have revealed that glycine can replace l-alanine in position 1 and d-alanine residues in positions 4 and 5 of the peptide subunit. Replacement of l-alanine in position 1 of the peptide subunit together with an accumulation of uridine diphosphate-muramic acid (UDP-MurNAc), indicating an inhibition of the UDP-MurNAc:l-Ala ligase, has been found in three bacteria (Staphylococcus aureus, Lactobacillus cellobiosus and L. plantarum). However, discrimination against precursors with glycine in position 1 in peptidoglycan synthesis has been observed only in S. aureus. Replacement of d-alanine residues was most common. It occurred in the peptidoglycan with one exception in all strains studied. In Corynebacterium sp., C. callunae, L. plantarum, and L. cellobiosus most of the d-alanine replacing glycine occurs C-terminal in position 4, and in C. insidiosum and S. aureus glycine is found C-terminal in position 5. It is suggested that the modified peptidoglycan precursors are accumulated by being poor substrates for some of the enzymes involved in peptidoglycan synthesis. Two mechanisms leading to a more loosely cross-linked peptidoglycan and to morphological changes of the cells are considered. First, the accumulation of glycine-containing precursors may lead to a disrupture of the normal balance between peptidoglycan synthesis and controlled enzymatic hydrolysis during growth. Second, the modified glycine-containing precursors may be incorporated. Since these are poor substrates in the transpeptidation reaction, a high percentage of muropeptides remains uncross-linked. The second mechanism may be the more significant in most cases.

Alanine↗