Search PubMed⌕ Search

Biomedical subjects

C Jacobsen

Publications and source records attributed to C Jacobsen.

At least 91 records · Page 5Linked to original sources
PubMed1989

Inhibition by glucosamine of myristoylation in human H9 lymphocytes and rat liver cells.

N-Myristoyl transferase (NMT) activity was measured in rat liver and H9 cells using an in vitro assay based on acylation of synthetic peptides. Glucosamine was found to inhibit the NMT activity. Using a synthetic peptide mimicking the N-terminus of HIV p27nef a Km value of 2.4 microM and a Vmax of 240 pmol/mg per h was found. In the presence of glucosamine the Vmax was lowered indicating that glucosamine acted as a non-competitive inhibitor. Glucosamine also inhibited incorporation of radiolabelled myristic acid into H9 cell proteins in vivo. In liver cells using a peptide from the N-terminus of p60 SRC only the Vmax was affected.

Acylation↗
PubMed1989

Electrogenic uptake of D-imino acids by luminal membrane vesicles from rabbit kidney proximal tubule.

Some characteristics of electrogenic uptake of D-proline and hydroxy-D-proline by luminal membrane vesicles isolated either from pars convoluta or from pars recta of rabbit proximal tubule were indirectly studied by the spectrophotometric method. In vesicles from pars convoluta, the uptake of D-imino acids was mediated by both Na+-dependent and Na+-independent, but electrogenic processes. Indirect evidence for coupling between D-imino acids and H+ fluxes was obtained by the following observations: (1) Addition of the H+ ionophore (FCCP) to the vesicle-dye (3,3'-diethyloxadicarbocyanine iodide) suspension completely abolished the Na+-independent electrogenic uptake of D-proline and hydroxy-D-proline by membrane vesicles from pars convoluta. (2) Addition of a relatively low concentration of D-proline in the incubation system decreased the H+-gradient dependent renal uptake of radioactive L-proline to approx. 60% of the control value. By contrast, the uptake of D-proline in vesicles from pars recta was strictly Na+-dependent, since no transient depolarization of membrane vesicles was ever observed in the absence of Na+. A comparison between the transport characteristics of D-imino acids and their naturally occurring L-isomers indicated that these compounds probably share common transport systems located along the proximal tubule of rabbit kidney.

Animals↗
PubMed1989

Potassium channels in the luminal membrane of rabbit proximal straight tubule. Evidence from vesicle studies.

The characteristics of 86Rb+ fluxes through K+ channels in luminal-membrane vesicles isolated from the pars recta of rabbit proximal tubule were studied. In KCl-loaded vesicles from the pars recta, transient accumulation of 86Rb+ is observed which is modestly inhibited by BaCl2 and blocked by CdCl2. The isotope accumulation is driven by an electrical diffusion potential, as shown in experiments using either these membrane vesicles loaded with different anions, or an outwardly directed Li+ gradient with a Li+ ionophore. The vesicles containing the channel show a cation selectivity with the order K+ greater than Rb+ greater than choline+ greater than or equal to Li+ greater than Na+. The CdCl2-sensitive 86Rb+ flux is dependent on intravesicular Ca2+. Increasing concentrations of Ca2+ gradually decreased the 86Rb+ uptake and at 1 microM-Ca2+ the CdCl2-sensitive isotope flux is nearly abolished.

Animals↗
PubMed1989

Ba2+-sensitive K+ channels in luminal-membrane vesicles from pars convoluta of rabbit proximal tubule.

This paper describes properties of 86Rb+ fluxes through a novel K+ channel in luminal-membrane vesicles isolated from pars convoluta of rabbit proximal tubule. The uptake of 86Rb+ into potassium salt loaded vesicles was specifically inhibited by Ba2+. The isotope accumulation is driven by an electrical diffusion potential as shown in experiments using these membrane vesicles loaded with anions of different membrane permeability and was as follows: gluconate greater than SO4(2-) greater than Cl-. Furthermore, the vesicles containing the channels show a cation selectivity with the order K+ greater than Rb+ greater than Li+ greater than Na+ = choline+.

Animals↗
PubMed1988

Demonstration of Na+-selective channels in the luminal-membrane vesicles isolated from pars recta of rabbit proximal tubule.

Characteristics of 22Na+ fluxes through Na+ channels in luminal-membrane vesicles isolated from either pars recta or pars convoluta of rabbit proximal tubule were studied. In NaCl-loaded vesicles from pars recta, transient accumulation of 22Na+ is observed, which is inhibited by amiloride. The isotope accumulation is driven by an electrical diffusion potential as shown in experiments using either these membrane vesicles loaded with different anions, or an outwardly directed K+ gradient with a K+ ionophore valinomycin. The vesicles containing the channel show a cation selectivity with the order Li+ greater than Na+ greater than K+. The amiloride-sensitive 22Na+ flux is dependent on intravesicular Ca2+. In NaCl-loaded vesicles from pars convoluta, no overshoot for 22Na+ uptake is observed. Furthermore, addition of amiloride to the incubation medium did not influence the uptake of 22Na+ in these vesicle preparations. It is concluded that Na+ channels are only present in pars recta of rabbit proximal tubule.

Amiloride↗
PubMed1988

Transport of L-proline by luminal membrane vesicles from pars recta of rabbit proximal tubule.

The mechanism of renal transport of L-proline by luminal membrane vesicles prepared from proximal straight tubules (pars recta) of rabbit kidney was investigated. The following picture emerges from transport studies: an electrogenic and Na+-requiring system confined to this region of nephron exists for transport of L-proline with a high affinity (Km = 0.16 mM) and low capacity (Vmax = 3.5 nmol.mg protein-1.15 S-1). Lowering the pH from 7.5 to 5.5 increased the affinity (Km lowered from 0.16 mM at pH 7.5 to 0.08 mM at pH 5.5) without changing the maximal capacity of this system. Modification of histidyl residues of the intact luminal membrane vesicles by diethyl-pyrocarbonate (DEP) completely abolished the transient renal accumulation of L-proline. Simultaneous presence of Na+ and L-proline (10 mM) protects against DEP inactivation of renal transport of radioactive L-proline. We propose that a histidyl residue may be at or close to the active site of L-proline transporter in vesicles from the pars recta.

Animals↗
PubMed1988

Emigration from Israel 1950-1981: a simulation study.

"Using our mathematical model of a general theory of normative regulation, we have reproduced over 80% of the variance in the cumulative percentages of emigrants [from Israel], as well as the yearly percentages from 1950 to 1981. These results suggest that, except for a limited period following the 'Six-Day War' of 1967, no situation-specific explanations are needed to account for the trends in emigration from Israel, and the phenomenon can be adequately accounted for by the general theory of normative regulation in modern industrialized societies. Some practical conclusions to mitigate the process are drawn from these findings."

Asia↗
PubMed1987

X-ray holograms at improved resolution: a study of zymogen granules.

X-ray holography offers the possibility of three-dimensional microscopy with resolution higher than that of the light microscope and with contrast based on x-ray edges. In principle, the method is especially advantageous for biological samples if x-rays in the wavelength region between the carbon and oxygen K edges are used. However, until now the achieved resolution has not exceeded that of the light microscope because of the poor coherence properties of the x-ray sources and the low resolution of the detectors that were available. With a recently developed x-ray source based on an undulator on an electron storage ring, and high resolution x-ray resist, a hologram has been recorded at about 400-angstrom resolution. The experiment utilized x-rays with wavelengths of 24.7 angstroms and required a 1-hour exposure of the pancreatic zymogen granules under study.

Animals↗
PubMed1987

Quantitative imaging and microanalysis with a scanning soft x-ray microscope.

A scanning soft x-ray microscope has been developed that uses synchrotron radiation focused by a Fresnel zone plate to form a submicron beamspot on the specimen. Transmitted x-rays are detected and used to form a quantitative map of specimen absorptivity. Applications of the instrument to the imaging of whole wet cells and to the mapping of calcium in sections of bone are presented, with a resolution of 300 nm and an elemental sensitivity of 2 micrograms cm-2.

Animals↗
PubMed1987

H+-L-proline cotransport by vesicles from pars convoluta of rabbit proximal tubule.

The mechanism of renal transport of L-proline by luminal-membrane vesicles isolated from proximal convoluted tubules of rabbit kidney was studied. It was found that H+ gradient (extravesicular greater than intravesicular) can drive the transport of L-proline into the vesicles both in the presence and absence of Na+. The stimulation of L-proline uptake by a pH gradient was additive with that produced by Na+. Saturation kinetic experiments revealed that pH gradient, in addition to Na+, increased the maximal uptake of L-proline by twofold. This is the first demonstration of H+-L-proline cotransport across luminal membrane of rabbit kidney proximal convoluted tubule. The physiological importance of this system is briefly discussed.

Animals↗
PubMed1986

Na+-H+ exchange in luminal-membrane vesicles from rabbit proximal convoluted and straight tubules in response to metabolic acidosis.

Na+-H+-exchanger activity of pars convoluta and pars recta luminal-membrane vesicles prepared from the proximal tubule of acidotic and control rabbits were assayed by a rapid-filtration technique and an Acridine Orange method. Both experimental approaches revealed the existence of an antiporter, sensitive to metabolic acidosis, in pars convoluta membrane vesicles. Kinetic data, obtained with the pH-sensitive dye, showed that the Km for Na+ transport was unchanged by acidosis, whereas Vmax. for exchanger activity was increased, on an average, by 44%. The fluorescence method, in contrast with the rapid-filtration technique, was able to detect exchanger activity in pars recta membrane vesicles. The Km value for the antiporter located in pars recta is comparable with that calculated for pars convoluta membrane vesicles. By contrast, the Vmax. of this exchanger is only about 25% of that found for pars convoluta. Furthermore, metabolic acidosis apparently does not increase Na+-H+-exchanger activity of pars recta luminal-membrane vesicles.

Acidosis, Renal Tubular↗
PubMed1986

Characteristics of D-galactose transport systems by luminal membrane vesicles from rabbit kidney.

The characteristics of renal transport of D-galactose by luminal membrane vesicles from either whole cortex, pars recta or pars convoluta of rabbit proximal tubule were investigated by a spectrophotometric method using a potential-sensitive carbocyanine dye. Uptake of D-galactose by luminal membrane vesicles prepared from whole cortex was carried out by an Na+-dependent and electrogenic process. Eadie-Hofstee analysis of saturation-kinetic data suggested the presence of multiple transport systems in vesicles from whole cortex for the uptake of D-galactose. Tubular localization of the transport systems was studied by the use of vesicles derived from pars recta and pars convoluta. In pars recta, Na+-dependent transport of D-galactose and D-glucose occurred by means of a high-affinity system (half-saturation: D-galactose, 0.15 +/- 0.02 mM; D-glucose, 0.13 +/- 0.02 mM). These results indicated that the "carrier' responsible for the uptake of these hexoses does not discriminate between the steric position of the C-4 hydroxyl group of these two isomers. This is further confirmed by competition experiments, which showed that D-galactose and D-glucose are taken up by the same and equal affinity transport system by these vesicle preparations. Uptake of D-galactose and D-glucose by luminal membrane vesicles isolated from pars convoluta was mediated by a low-affinity common transport system (half-saturation: D-galactose, 15 +/- 2 mM; D-glucose, 2.5 +/- 0.5 mM). These findings strongly suggested that the "carrier' involved in the transport of monosaccharides in vesicles from pars convoluta is specific for the steric position of the C-4 hydroxyl group of these sugars and presumably interacts only with D-glucose at normal physiological concentration.

Animals↗
PubMed1984

Isolation and partial purification of dicarboxylic acid binding protein from luminal-membrane vesicles of rabbit kidney cortex.

A specific dicarboxylic acid binding protein was isolated by solubilizing highly purified renal luminal-membrane vesicles with the non-ionic detergent C12E8 , followed by affinity chromatographic procedures. SDS-polyacrylamide gel electrophoresis of the samples containing dicarboxylic acid binding protein showed a single sharp band of an apparent molecular weight of 50 000. After treatment with mercaptoethanol the protein was split in two subunits of apparent molecular weights of 35 000 and 15 000. By analytical ultracentrifugation the minimal molecular weight of the dicarboxylic acid binding protein preparation was calculated to be 54 000. Binding of the radioactive succinate and L-malate to the dicarboxylic acid binding protein preparation as studied by equilibrium dialysis showed saturation phenomenon and was specifically inhibited by addition of D-malate. The dissociation constants for succinate (0.18 mM) and L-malate (0.33 mM) calculated from the binding data agree extremely well with the apparent Km values for these organic acids found in transport studies utilizing intact luminal-membrane vesicles.

Animals↗
PubMed1984

Renal transport of neutral amino acids. Tubular localization of Na+-dependent phenylalanine- and glucose-transport systems.

The transport properties for phenylalanine and glucose in luminal-membrane vesicles from outer cortex (pars convoluta) and outer medulla (pars recta) of rabbit kidney were studied by a spectrophotometric method. Uptake of phenylalanine as well as of glucose by the two types of membrane vesicles was found to be Na+-dependent, electrogenic and stereospecific. Na+-dependent transport of L-phenylalanine by outer-cortical membrane vesicles could be accounted for by one transport system (KA congruent to 1.5 mM). By contrast, in the outer-medullary preparation, L-phenylalanine transport occurred via two transport systems, namely a high-affinity system with K1A congruent to 0.33 mM and a low-affinity system with K2A congruent to 7 mM respectively. Na+-dependent uptake of D-glucose by pars convoluta and pars recta membrane vesicles could be described by single, but different, transport systems, namely a low-affinity system with KA congruent to 3.5 mM and a high-affinity system with KA congruent to 0.30 mM respectively. Attempts to calculate the stoichiometry of the different Na+/D-glucose transport systems by using Hill-type plots revealed that the ratio of the Na+/hexose co-transport probably is 1:1 in the case of pars convoluta and 2:1 in membrane vesicles from pars recta. The Na+/L-phenylalanine stoichiometry of the pars convoluta transporter probably is 1:1. Both the high-affinity and the low-affinity Na+-dependent L-phenylalanine transport system of pars recta membrane vesicles seem to operate with a 1:1 stoichiometry. The physiological importance of the arrangement of low-affinity and high-affinity transport systems along the kidney proximal tubule is discussed.

Animals↗
PubMed1984

Binding properties of monoclonal anti-IgG antibodies: analysis of binding curves in monoclonal antibody systems.

The binding properties of an immune complex-forming system comprising human IgG and mouse monoclonal antibodies against human IgG have been studied. A refined binding assay has been applied directly on ascitic fluid containing monoclonal antibody. Complete sets of binding data of a series of different monoclonal antibodies were collected and analysed by various graphical and statistical methods. Special attention was given to methods which allow determination of specific monoclonal antibody concentration as well as antibody affinity. It was found that the formation of genuine antigen: antibody complexes per se gives rise to deviations from expected linearity in commonly used binding equations. Good correlation was found between the antibody concentrations obtained by various graphical approaches, whereas the size of the association constant seemed to depend on the method in use. The binding pattern was found to be dependent on the concentration of antibody. Most reliable parameters were obtained if the product of the antibody concentration and the association constant was below 10.

Animals↗