PubMed Health⌕ Search

Biomedical subjects

J M Steim

Publications and source records attributed to J M Steim.

At least 19 recordsLinked to original sources
PubMed1990

Lipid conjugates of antiretroviral agents. I. Azidothymidine-monophosphate-diglyceride: anti-HIV activity, physical properties, and interaction with plasma proteins.

3'-Azido-3'-deoxythymidine-5'-phosphate diglyceride (16:0/18:1 omega 9), a phosphatic acid conjugate of AZT, is active against HIV replication in H9 cells and syncytia formation in MOLT-3 cells. The activities rank as AZT greater than pure conjugate greater than conjugate in mixed liposomes, with the pure conjugate having about one-third the activity of free AZT. The compound binds very rapidly to serum lipoproteins, but not to serum albumin, alpha and beta globulins, or red cells. Pancreatic phospholipase A2 hydrolyzes it to the lysophosphatidic acid conjugate.

Antiviral Agents↗
PubMed1990

Lipid conjugates of antiretroviral agents. II. Disodium palmityl phosphonoformate: anti-HIV activity, physical properties, and interaction with plasma proteins.

Disodium palmityl phosphonoformate, a novel lipid phosphoester of the anti HIV agent phosphonoformate (foscarnet), inhibits HIV replication in H9 cells and syncytia formation in MOLT-3 cells as effectively as foscarnet itself, as shown by dose-response data from assays for expression of p17 and p24 viral antigens and syncytia formation. Protein binding studies indicate that in serum, the derivative exists bound to albumin and the lipoproteins, and would therefore be likely to exhibit improved serum lifetime in vivo.

Antiviral Agents↗
PubMed1988

Micellization of fatty acyl-CoA mixtures and its relevance to the fatty acyl selectivity of acyltransferases.

The critical micelle concentrations (CMCs) of palmitoyl-CoA/stearoyl-CoA and palmitoyl-CoA/oleoyl-CoA mixtures in 0.050 M KPi, pH 7.4, a buffer used in enzymatic studies, were determined by fluorescence. Mixed micelle solution theory, analogous to the thermodynamic treatment of vapor pressure, was applied to calculate monomer and micelle compositions. The behavior of the palmitoyl-CoA/stearoyl-CoA mixture is ideal, while the palmitoyl-CoA/oleoyl-CoA mixture, although not exhibiting ideal behavior, can be fitted reasonably well by nonideal theory. In both mixtures, selective micellization takes place and, unlike the case of pure fatty acyl-CoAs, above the CMC of the mixtures the concentration of molecules free in solution is strongly dependent upon total concentration. The information derived from the present physical studies becomes important in enzymatic studies with membrane-bound acyltransferases, where selectivity toward various fatty acyl donors, presented as binary mixtures, is frequently observed.

Acyl Coenzyme A↗
PubMed1986

Solubility of palmitoyl-coenzyme A in acyltransferase assay buffers containing magnesium ions.

The solubility of palmitoyl-CoA is strongly affected by Mg2+ concentrations commonly used in acyltransferase reactions. In 0.10 M Tris-HCl buffer at pH 7.4 or 8.5, all of the palmitoyl-CoA in 10 microM solutions and 90% of the palmitoyl-CoA in 100 microM solutions are precipitated by 1 mM Mg2+. In 0.05 M phosphate at pH 7.4, and in 0.10 M Tris-HCl containing 0.4 M KCl, the substrate remains soluble at Mg2+ concentrations below 4-5 mM. Above 5 mM Mg2+, palmitoyl-CoA is insoluble in all of these buffers. Substrate solubility could therefore be a limiting factor when free Mg2+ and fatty acyl-CoAs are present together during acyltransferase assays.

Acyl Coenzyme A↗
PubMed1985

Physical properties of fatty acyl-CoA. Critical micelle concentrations and micellar size and shape.

Critical micelle concentrations (CMCs) of palmitoyl-CoA were determined by surface tension, conductivity, and fluorimetric measurements in a variety of buffers at several pH values and ionic strengths. They ranged from 7 to 250 microM and were frequently an order of magnitude higher than most reported values. The CMCs of stearoyl-CoA and oleoyl-CoA, determined fluorimetrically, were also high and consistent with the expected effects of chain length and unsaturation. The effects of ionic strength and temperature were analyzed to obtain the extent of counterion binding and the thermodynamic parameters of micellization. The values of delta H0, delta G0, and delta S0 obtained in 0.011 M Tris, pH 8.3, are -6 K X J X mol-1, -64 K X J X mol-1, and +193 J X mol-1 X K-1, and the average number of univalent ions bound per molecule in the micelles is 1.4. These values are within the range of those obtained for other univalent and polyvalent detergents. Analyzed by sedimentation and diffusion, the micelles are approximately spherical with an anhydrous mass of 50,000 daltons but with dimensions inconsistent with fully extended molecules. Correlation of the information obtained from the present physical studies with kinetic studies using long-chain fatty acyl-CoAs as enzyme substrates may be helpful for understanding the enzymology of these compounds, and some previously published kinetic studies of membrane-bound and soluble enzymes may bear reinterpretation.

Acyl Coenzyme A↗
PubMed1985

Biophysical properties of cytidine diphosphate diacylglycerol in solution.

The physical properties of CDP diacylglycerol derived from egg phosphatidylcholine are very different from those of the common glycerophospholipids, such as phosphatidylcholine. Gently dispersed in buffer (5 mM phosphate, 0.15 M NaCl, pH 7.4), the liponucleotide initially forms an opalescent suspension of spherical vesicles, up to 50 micron in diameter, which appear to be unilamellar. These large vesicles are unstable and, independently of initial concentration, unstirred suspensions are no longer turbid after being incubated for about 1 h at room temperature. The passage of samples through Sepharose and Sephadex at increasing time intervals after the first hour reveals a continuing but slow diminution in size until, at about two days, a final peak is obtained which remains invariant for longer times. Chromatography of these ultimate stable micelles on Sephadex G-200 gives a Stokes radius of 4.2 nm. Their sedimentation coefficient extrapolated to zero concentration is 6.1 S. These numbers, combined with a partial specific volume of 0.835 ml X g-1, give an anhydrous mass of 155 000 Da and an aggregation number of 158. Although the data suggest the particles to be spherical, other compact forms cannot be excluded. Proton NMR at 220 MHz shows time-dependent spectral changes which are consistent with the slow structural transformation observed by gel-filtration chromatography, and indicate that the sugar and cytosine groups in the ultimate micelles apparently are motionally restricted. The critical micelle concentration is near 6 microM, but micelle-free molecule equilibration requires at least 7 days at a total concentration of 89 microM. Sonication considerably decreases the time required for the vesicle-micelle transformation and the micelle-free molecule equilibration. Some implications for enzymology are discussed.

Biophysical Phenomena↗
PubMed1982

The physical state of quick-frozen membranes and lipids.

Lipid bilayers and biomembranes produce nearly identical calorimeter scans regardless of whether they are slowly cooled under near-equilibrium conditions or rapidly frozen at rates used in freeze-fracture electron microscopy. Except for the melting of ice at 273 K, for both cooling regimens no significant thermal events occur from 100 K to the usual gel to liquid crystal transition. The gel to liquid crystal transition itself is somewhat altered by rapid cooling when bilayers contain mixed lipid species. Combined with X-ray diffraction studies, the results indicate that quickly frozen bilayers are crystalline, but that the crystalline domains are quite small or otherwise disordered. In contrast to the behavior of lipids in bilayers, hexagonal-phase calcium cardiolipin easily forms a glass upon cooling.

Animals↗
PubMed1982

Physical properties of arabinofuranosylcytosine diphosphate diacylglycerol, an antitumor liponucleotide.

Dispersed from a dry film into buffer (5 mM phosphate, 0.15 M NaCl, pH 7.4), the liponucleotide 1-beta-D-arabinofuranosylcytosine 5'-diphosphate L-1,2-diacylglycerol (ara-CDPdiacylglycerol) spontaneously forms vesicles which are several microns in diameter and probably unilamellar. Their average size immediately begins to decrease, and after 2 h none can be seen in the light microscope. During 1-2 days in unstirred solutions at 25 degrees C, the vesicles are transformed to spherical or nearly spherical micelles having an apparent partial specific volume of 0.835 ml . g-1, a maximum possible aggregation number of about 150, and an anhydrous radius of about 37 A. The critical micelle concentration (CMC) is about 10 microM in buffer and 20 microM in distilled water, but micelle-monomer equilibration requires at least 1 week at a total concentration of 66 microM. This exceedingly slow equilibration is unique among reported detergents. The standard enthalpy and entropy of micellization are - 13 kJ . mol-1 and 87 J . mol-1 . K-1, respectively. These values are within the range reported for other detergents. Sonication accelerates the vesicle-micelle transformation to 30 min.

Chemical Phenomena↗
PubMed1980

Dilatometry of dipalmitoyllecithin-cholesterol bilayers.

The interactions of cholesterol and dipalmitoyl-phosphatidylcholine in bilayers were investigated by differential scanning dilatometry and related techniques. Dipalmitoyl-phosphatidylcholine bilayers ranging from 0 to 50 mol % cholesterol were studied over a temperature range of 0-50 degrees C. These investigations allowed construction of a three-dimensional surface with dimensions of mole fraction of cholesterol, temperature, and apparent partial specific volume. Much of the phenomenology reported for dipalmitoylphosphatidylcholine and dipalmitoylphosphatidylcholine-cholesterol bilayers appears and can be interrelated on this surface. In addition to the thermotropic events associated with the system, two cholesterol-induced events at 17.5-20 and 29 mol % cholesterol are particularly in evidence.

Cholesterol↗
PubMed1980

A phosphatidylinositol-containing derivative of Lactobacillus casei ATCC 7469.

A derivative of Lactobaccillus casei ATCC 7469, characterized by limited growth in liquid media and an unusual phospholipid composition, has been isolated. Grown to early stationary phase on a lipid-free and inositol-free medium, the organism produces phosphatidylinositol phosphatidylglycerol, and diphosphatidylglycerol. The phosphatidylinositol was identified by thin-layer, paper, and gas chromatography, and by mass spectrometry. In agreement with published data, the conventional strain produced phosphatidylglycerol, diphosphatidylglycerol, and lysylphosphatidylglycerol, but no phosphatidylinositol. The phospholipid/glycolipid molar ratio, calculated on the basis of published glycolipid analyses, is 1.3 : 1 for the derivative and 1.5 : 1 for the conventional strain.

Lacticaseibacillus casei↗
PubMed1980

Cytotoxic liponucleotide analogs. II. Antitumor activity of CDP-diacylglycerol analogs containing the cytosine arabinoside moiety.

Among events limiting the effectiveness of cancer chemotherapy are the general lack of preferential uptake of anticancer drugs by tumor cells and the occurrence of drug resistance. An approach has been undertaken to explore whether or not such events can be favorably altered or circumvented therapeutically by development of a new class of anticancer molecules, cytotoxic liponucleotide analogs. The design of cytotoxic liponucleotide analogs encompasses both biochemical and biophysical aspects of liponucleotide and glycerophospholipid structure and metabolism. Several cytotoxic liponucleotide analogs of cytidine diphosphate diacylglycerol (CDPdiacylglycerol/dCDPdiacylglycerol), containing the 1-beta-D-arabinofuranosyl moiety, were tested for antitumor activity. Multispecies ara-CDPdiacylglycerol (1-beta-D-arabinofuranosylcytosine 5'-diphosphate diacylglycerol), which contains egg lecithin-derived mixed fatty acyl chains, was more active than 1-beta-D-arabinofuranosylcytosine (ara-C), a clinically used anticancer drug, against leukemia L5178Y and P388 ascites cells in mice. At identical single doses (50 mg/kg per day times 4) administered intraperitoneally, ara-CDPdiacylglycerol prolonged the life spans of L5178Y tumor-bearing mice 93%, while ara-C prolonged life by 18%. Ara-CDPdiacylglycerol increased life spans of P388 tumor-bearing mice by 357% at doses of 50 mg/kg per day times 4; the maximum increase with ara-C was 159% (85 mg/kg per day times 4). Against a P388 ara-C-resistant cell line (P/Ara-C, kinase deficient) in mice, ara-CDPdiacylglycerol prolonged survival times by 34% at a dose of 50 mg/kg per day times 4 and by 55% at 75 mg/kg per day times 4; the drug was not active against two other ara-C-resistant murine leukemia mutants (CA 55, CA5b). With cell line-derived human colon carcinoma HCT-15 grown in mice immunosuppressed with anti-thymocyte serum, ara-CDPdiacylglycerol at a single daily dose of 50 mg/kg per day times 4 significantly reduced tumor weights to 21% of the controls; the same dose schedule of ara-C caused no observable reduction of tumor weights. Results of these preliminary antitumor evaluations indicate that cytotoxic liponucleotide analogs should be investigated further to determine their potential as antineoplastic molecules.

Animals↗
PubMed1977

Control of fatty acid composition of Acholeplasma laidlawii membranes.

The temperature-dependent pattern of incorporation of palmitate and oleate from the growth medium into Acholeplasma laidlawii membrane lipids correlates with the physical state of the membrane defined by calorimetry. Both the pattern and the state can be changed at will by changing the fatty acid composition of the membrane lipids. The ratio of palmitate to oleate incorporated is independent of temperature when the membrane bilayer is below its transition and fully ordered, but becomes temperature dependent upon the onset of the transition and continues to be temperature dependent when the membrane is above its transition and fully fluid. This behavior is mimicked by the physical binding of palmitate and oleate to bilayers of extracted membrane lipids and to bilayers of lecithin. Selective binding by membranes may provide a means for controlling lipid fatty acid composition without invoking an enzymatic mechanism.

Acholeplasma laidlawii↗