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Biomedical subjects

H Timmerman

Publications and source records attributed to H Timmerman.

At least 253 records · Page 14Linked to original sources
PubMed1984

The ionization of beta-adrenoceptor agonists: a method for unravelling ionization schemes.

To investigate the ionization schemes of beta-adrenoceptor agonists, a combined electrochemical/uv-spectrophotometric method with computer-assisted data-analysis was developed, yielding the macroscopic and microscopic ionization constants. From the four species possible, cations and zwitterions were found the main species present at physiological pH, the formation of uncharged molecules and anions being less favourable or apparently negligible.

Adrenergic beta-Agonists↗
PubMed1983

Determination of formation constants of copper(II) complexes of Adler medium components with a solid-state copper(II) ion-selective electrode.

A general method for the determination of overall conditional formation constants of copper(II) complexes of mycoplasma growth medium (Adler) constituents together with the protonation constants of the complexing ligands was developed. In Adler medium a total of 0.204 +/- 0.004 molar copper binding sites proved to be present with log beta 2 = 8.14 +/- 0.05 (mu = 0.11) and log Ka = 6.14 +/- 0.004. Conditional overall formation constants were calculated at various pH values. Free copper(II) ion concentrations were calculated as a function of the total added amount of copper(II) and pH. The consequences of these findings for the determination of the growth inhibition of mycoplasmas by copper complexes of 2,2'-bipyridyl analogues are stressed.

Chemical Phenomena↗
PubMed1982

Mechanism of action of the copper(I) complex of 2,9-dimethyl-1,10-phenanthroline on Mycoplasma gallisepticum.

Evidence was found that the inhibitory action of Cu(DMP)2NO3, the copper(I) complex of 2,9-dimethyl-1,10-phenanthroline (DMP), on Mycoplasma gallisepticum is a consequence of the ultimate toxicity of copper, and not that of the ligand, DMP. From uptake studies with radiolabeled 67Cu and [14C]DMP, we concluded that significantly more copper than DMP is bound to the mycoplasmal cell. It appeared that dissociation of Cu(DMP)2+ occurred shortly after interaction with the cell membrane. Copper was transported across the cytoplasmic membrane. A strong dependence of copper uptake on the incubation medium was observed in the absence of DMP. The main function of the ligand DMP appeared to be as a vehicle for the transport of copper from nontoxic copper-medium complexes to membrane-buried cellular ligands.

Cell Membrane↗
PubMed1981

Mode of action of the copper(I) complex of 2,9-dimethyl-1,10-phenanthroline on Mycoplasma gallisepticum.

Various physiological important activities of Mycoplasma gallisepticum were inhibited by the copper(I) complex of 2,9-dimethyl-1,10-phenanthroline [Cu(DMP)2NO3]. The energy-yielding metabolism was inhibited because the conversion of pyruvate into lactate was found to be blocked by Cu(DMP)2NO3, indicating a selective inhibition of lactate dehydrogenase. Also, the production rate of acetate and the rate of oxygen uptake by whole cells of M. gallisepticum appeared to be strongly decreased. Experiments with crude cell extracts showed an inhibition of reduced nicotinamide adenine dinucleotide (NADH) oxidase by Cu(DMP)2NO3 and an even stronger inhibition of NADH oxidase and lactate dehydrogenase by CuSO4. No preferential inhibition of adenosine 5'-triphosphatase and pyruvate kinase was found. Investigations on the influence of Cu(DMP)2NO3 on deoxyribonucleic acid, ribonucleic acid, and protein synthesis with growing cells of M. gallisepticum showed a selective inhibition of the incorporation of [14C]thymidine into deoxyribonucleic acid. Cu(DMP)2NO3 induced a decrease in the total amount of accessible sulfhydryl groups of whole cells of M. gallisepticum, indicating that the observed diverse toxicity of Cu(DMP)2NO3 may be associated with the interaction of copper ions with protein sulfhydryl groups.

Copper↗