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Biomedical subjects

G M Roomans

Publications and source records attributed to G M Roomans.

At least 199 records · Page 11Linked to original sources
PubMed1979

Kinetics of Ca2+ and Sr2+ uptake by yeast. Effects of pH, cations and phosphate.

The uptake of Ca2+ and Sr2+ by the yeast Saccharomyces cerevisiae is energy dependent, and shows a deviation from simple Michaelis-Menten kinetics. A model is discussed that takes into account the effect of the surface potential and the membrane potential on uptake kinetics. The rate of Ca2+ and Sr2+ uptake is influenced by the cell pH and by the medium pH. The inhibition of uptake at low concentration of Ca2+ and Sr2+ at low pH may be explained by a decrease of the surface potential. The inhibition of Ca2+ and Sr2+ uptake by monovalent cations is independent of the divalent cation concentration. The inhibition shows saturation kinetics, and the concentration of monovalent cation at which half-maximal inhibition is observed, is equal to the affinity constant of this ion for the monovalent cation transport system. The inhibition of divalent cation uptake by monovalent cations appears to be related to depolarization of the cell membrane. Phosphate exerts a dual effect on uptake of divalent cations: and initial inhibition and a secondary stimulation. The inhibition shows saturation kinetics, and the inhibition constant is equal to the affinity constant of phosphate for its transport mechanism. The secondary stimulation can only partly be explained by a decrease of the cell pH, suggesting interaction of intracellular phosphate, or a phosphorylated compound, with the translocation mechanism.

Biological Transport, Active↗
PubMed1979

Kinetics of sulfate uptake by yeast.

Uptake of sulfate by yeast requires the presence of a metabolic substrate and is dependent on the time during which the cells have been metabolizing in the absence of sulfate. At low concentrations of sulfate, uptake can be described by simple saturation kinetics. Uptake of sulfate is accompanied by a net proton influx of 3 H+ and an efflux of 1 K+ for each sulfate ion taken up. Divalent cations stimulate sulfate uptake at low concentrations of sulfate; the maximal rate of uptake is not significantly affected but Km is lowered. Stimulation by divalent cations shows an optimum at a cation concentration of about 4 mM. Monovalent cations are less effective, trivalent cations are more effective in stimulating sulfate uptake. The results are qualitatively in accordance with the notion, that the effect of cations is due to an effect via the surface potential.

Biological Transport↗
PubMed1979

Quantitative X-ray microanalysis of halogen elements in biological specimens.

Standards were prepared for quantitative X-ray microanalysis of the halogen elements Cl, Br and I in sections of resin embedded biological specimens. Halogenated aromatic compounds were dissolved in resin, which subsequently was polymerized. Homogeneity and stability of the standards were determined and found to be satisfactory. A general procedure of calculation of elemental concentrations according to the continuum method is given for the case that the specimen contains appreciable concentrations of one or more rather heavy elements. It is shown that use of approximations may lead to unacceptable errors, even in the concentration ranges occurring in biological specimens. As a practical application, the concentration of bromine in the chloroplasts of the red alga Chondrus crispus was determined quantitatively. The inner cells contained more bromine than the epidermal cells: in the chloroplasts of the inner cells bromine concentrations of about 6% could be demonstrated.

Bromine↗
PubMed1979

Mercury-induced loss of K+ from yeast cells investigated by electron probe x-ray microanalysis.

According to Passow & Rothstein (1960), the mercury-induced loss of K+ from yeast cells is an all-or-none effect. This hypothesis was tested by analysing individual yeast cells by means of energy-dispersive X-ray microanalysis. A dual effect of mercury was observed. The cell population was split into two parts: one part consisted of cells that had suffered a (nearly) complete loss of K+- the number of these cells increased with increasing concentrations of HgCl2; the other consisted of cells that had only lost part of their K+ content--these cells showed a normal distribution around a central value that decreased with increasing concentrations of HgCl2. Our analysis shows that the effect of mercury is more complex than originally suggested and that, in addition to an all-or-none effect, a gradual loss of K+ occurs.

Copper↗
PubMed1978

Electron probe X-ray microanalysis of human muscle biopsies.

The elemental composition of human muscle fibres have been determined by electron probe microanalysis. In order to distinguish between different types of fibres, two approaches were used. In one approach individual fibres were isolated, portions of them used for a typing by histochemical methods and the main part used for X-ray microanalysis. In the other approach the muscle biopsy was serial-sectioned, some sections used for a histochemical typing and the others (16 micrometer thick cryosections) used for X-ray microanalysis in th eelectron microscopy. The comparison of the ratios between P, S and K in Study No. 1 and 2 indicates different concentrations of sulphur in the subsarcolemmal zone and in the interior of the fibre. Both routes give information on all elements (except the ten lightest ones) contained in the fibres or in sections of them, provided the concentration is high enough. In order to obtain quantitative data, expressed as mmol/kgw, the spectra of the specimens were compared to those of standards of known composition and the data subjected to a so called ZAF-correction (corrections for the atomic number effect, absorption of X-rays in the specimen and secondary fluorescence). Quantitative data concerning phosphorus, sulphur, chlorine and potassium were obtained in Study No. 2. A significantly higher sulphur concentration was found in type IIA muscle fibres as compared to those of type I.

Chlorine↗
PubMed1978

Electrolytes in nails analysed by X-ray microanalysis in electron microscopy. Considerations on a new method for the diagnosis of cystic fibrosis.

Patients with cystic fibrosis (CF) have an increased concentration of sodium in their nails. Hitherto, only neutron activation analysis has been considered for the diagnosis of cystic fibrosis by analysis of electrolytes in nails. It has been thoroughly tested methodologically and clinically. However, the intrinsic advantages of X-ray microanalysis and the results obtained in this study suggest that this method, after further testing, may be a useful diagnostic acid for cystic fibrosis. In comparison with neutron activation analysis, X-ray microanalysis has the advantage of simultaneously giving the concentrations of several elements and may be accessible at any hospital with an electron microscope fitted with the necessary equipment. Nails of CF-patients are here shown to have increased concentrations of Na, K and Cl, which will make the diagnosis of cystic fibrosis more reliable. The possibility of using sulphur as a reference element may eliminate the weighing procedure necessary in neutron activation analysis.

Child, Preschool↗
PubMed1977

Interaction of phosphate with monovalent cation uptake in yeast.

The uptake of monovalent cations by yeast via the monovalent cation uptake mechanism is inhibited by phosphate. The inhibition of Rb+ uptake shows saturation kinetics and the phosphate concentration at which half-maximal inhibition is observed is equal to the Km of phosphate for the sodium-independent phosphate uptake mechanism. The kinetic coefficients of Rb+ and TI+ uptake are affected by phosphate: the maximal rate of uptake is decreased and the apparent affinity constants for the translocation sites are increased. In the case of Na+ uptake, the inhibition by phosphate may be partly or completely compensated by stimulation of Na+ uptake via a sodium-phosphate cotransport mechanism. Phosphate effects a transient stimulation of the efflux of the lipophilic cation dibenzyldimethylammonium from preloaded yeast cells and a transient inhibition of dibenzyldimethylammonium uptake. Possibly, the inhibition of monovalent cation uptake in yeast can be explained by a transient depolarization of the cell membrane by phosphate.

Anaerobiosis↗
PubMed1977

Intracellular pH and the kinetics of Rb+ uptake by yeast non-carrier versus mobile carrier-mediated uptake.

The effect of changes in the intracellular pH upon the concentration dependence of the Rb+ uptake by yeast is investigated. It is shown, that the uptake of Rb+ can be described by a mechanism in which the total concentration of primary binding sites at the outer side of the membrane is independent of the intracellular ligand composition and of the membrane potential, and the influx rate constants depend upon the intracellular pH and/or upon the membrane potential. It is argued that the involvement of a mobile carrier mechanism is not likely.

Anaerobiosis↗
PubMed1977

Cotransport of phosphate and sodium by yeast.

Phosphate uptake by yeast at pH 7.2 is mediated by two mechanisms, one of which has a Km of 30 micronM and is independent of sodium, and a sodium-dependent mechanism with a Km of 0.6 micronM, both Km values with respect to monovalent phosphate. The sodium-dependent mechanism has two sites with affinity for Na+, with affinity constants of 0.04 and 29 mM. Also lithium enhances phosphate uptake; the affinity constants for lithium are 0.3 and 36 mM. Other alkali ions do not stimulate phosphate uptake at pH 7.2. Ribidium has no effect on the stimulation of phosphate uptake by sodium. Phosphate and arsenate enhance sodium uptake at pH 7.2. The Km of this stimulation with regard to monovalent orthophosphate is about equal to that of the sodium-dependent phosphate uptake. The properties of the cation binding sites of the phosphate uptake mechanism and those of the phosphate-dependent cation transport mechanism have been compared. The existence of a separate sodium-phosphate cotransport system is proposed.

Adenosine Triphosphate↗
PubMed1977

Organometallic and organometalloid compounds as standards for microprobe analysis of epoxy resin embedded tissue.

X-ray microanalysis of phosphorus, transition elements and heavy metals in biological tissue is frequently carried out on thin sections of specimens embedded in epoxy resin. A logical choice for the quantitive microprobe analysis of these specimens is a standard, consisting of a homogenous solution of the elements of interest in the epoxy resin. Four kinds of compounds were found suitable for this purpose: (1) phenyl compounds containing group Vb elements, (2) cyclopentadienyl-derivatives, (3) a pentanedione derivative (acetylacetonate) and (4) complexes of metals with dialkyldithiocarbamates. In the latter case, the standard also contains sulphur. Standards for P, Sb (1) Mn, Fe (2) Ni (3) Cu, Zn, Cd, Hg, Pb, Bi (4) were prepared in Epon 812 or Spurr epoxy resin. The compounds were mixed with the resin (without accelerator) to which some propylene oxide may be added, and dissolved immediately or after short heating. The maximal concentration of metal was in the order of magnitude of several promilles to 1%. Solubility in the Spurr resin was better than in Epon 812. After addition of the accelerator, polymerization was carried out as usual. The compounds used are commercially availalbe at low cost or can be easily prepared.

Alkanes↗
PubMed1976

Subcellular localization of diffusible ions in the yeast Saccharomyces cerevisiae: quantitative microprobe analysis of thin freeze-dried sections.

In yeast cells, of which the intracellular potassium had been partly replaced by rubidium or caesium, the intracellular ion distribution was studied by means of energy-dispersive X-ray microanalysis. The cells were rapidly frozen and thin sections were cut at low temperature on a cryo-ultramicrotome without the use of a trough liquid. By this dry cryosectioning procedure, complete retention of the diffusbile ions in the cells was obtained. Unless the sections had been exposed to moisture, no signs of redistribution were apparent. For quantitative determinations a gelatin standard, containing known amounts of the elements of interest, was prepared in the same way as the cells. The concentrations of potassium, rubidium, caesium and chloride in the nucleus, the cytoplasm and the vacuole could be measured. The intracellular distributions of potassium, rubidium and caesium were very similar. The concentrations of these ions in the cytoplasm were about equal to those in the nucleus and twice those in the vacuole. The total concentration in the cytoplasm was 180-190 mmol/kg fresh weight, in the nucleus 190-200 mmol/kg fresh weight and in the vacuole 75-90 mmol/kg fresh weight. The permeability of the yeast cell for chloride is markedly lower than for the cations.

Cell Nucleus↗
PubMedDate not supplied

Copper in green hair: a quantitative investigation by electron probe x-ray microanalysis.

Eleven cases of green hair were collected and hair tips were analyzed in the electron microscope by energy-dispersive x-ray microanalysis. In all cases, remarkable copper concentrations could be demonstrated (0.2-1.8% w/w). In normal hair the concentration of copper was below the detection limit (0.02% w/w). Analyses of hair cross sections showed a concentration gradient from the periphery toward the center, the periphery having higher values. This observation is in agreement with suspected contamination of the hair with copper from extraneous sources: analysis of the tapwater in patients' homes showed elevated copper concentrations. In addition, the water showed aggressive properties (pH outside the recommended range, high nitrate concentrations, heavily chlorinated). Investigations by transmission electron microscopy showed damage in the endocuticula. Experimental studies of normal unaffected hair fibers showed that treatment with a copper salt alone could result in binding of copper to the hair but that the extent of copper binding could be greatly increased by damaging the cuticula with chlorinated water. It is suggested that aggressive water attacks copper tubings leading to increased copper concentrations in tapwater and causes cuticular damage, which facilitates entry of copper into the hair.

Adolescent↗
PubMedDate not supplied

Electrolyte redistribution in cystic fibrosis fibroblasts studied by electron probe X-ray microanalysis.

The elemental composition of fibroblasts from cystic fibrosis (CF) patients and from healthy controls was compared by means of electron probe X-ray micro-analysis. Significantly lower sodium levels (p < .01) and higher calcium levels (p < .02) were found in CF fibroblasts, indicating a disturbance of ion regulation in these cells. Treatment with Staphylococcus aureus protein A and gammaglobulin (proteins that may influence the ciliotoxic CF factor) did not change the elemental composition of the fibroblasts.

Adolescent↗