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Biomedical subjects

M Bloom

Publications and source records attributed to M Bloom.

At least 37 records · Page 2Linked to original sources
PubMed1988

Affinity labeling of the allosteric activator site(s) of spinach leaf ADP-glucose pyrophosphorylase.

Pyridoxal-P has been shown to be an activator of the spinach leaf ADP-glucose pyrophosphorylase. It has a higher apparent affinity than the physiological activator 3-phosphoglycerate but only activates the enzyme activity 6-fold whereas 3-phosphoglycerate gives a 25-fold activation. Reductive phosphopyridoxylation of the spinach leaf enzyme results in enzyme having less dependence on the presence of activator for activity. Labeled pyridoxal-P is incorporated into both the 54- and 51-kilodalton subunits of the spinach leaf enzyme. The incorporation is inhibited by the presence of either 3-phosphoglycerate or the allosteric inhibitor, inorganic phosphate, thus suggesting that pyridoxal phosphate is covalently bound to the allosteric activator site. The pyridoxal phosphate is bound to an epsilon-amino group of a lysine residue. The phosphopyridoxylated enzyme is more resistant to phosphate inhibition than the unmodified form. The modified 51-kDa subunit has been digested with trypsin, and the peptide containing the labeled pyridoxal phosphate has been purified via high performance liquid chromatography and sequenced. Comparison of this sequence with the deduced amino acid sequence of a rice endosperm cDNA clone indicates that the putative allosteric site of the 51-kDa subunit is close to the carboxyl-terminal. This is in contrast to what had been demonstrated for the position of the activator site of the Escherichia coli ADP-glucose pyrophosphorylase which was shown to be close to the amino-terminal of the subunit.

Affinity Labels↗
PubMed1988

2H and 31P NMR study of pentalysine interaction with headgroup deuterated phosphatidylcholine and phosphatidylserine.

The interaction of cationic pentalysine with phospholipid membranes was studied by using phosphorus and deuterium Nuclear Magnetic Resonance (NMR) of headgroup deuterated dimyristoyl phosphatidylcholine (DMPC) and dimyristoyl phosphatidylserine (DMPS). In the absence of pentalysine, some of the deuterium and phosphorus spectra of DMPC/DMPS 5:1 (m:m) membranes gave lineshapes similar to those of partially-oriented bilayers with the planes of the bilayers being parallel to the magnetic field. The deuterium NMR data show that the quadrupolar splittings of the deuterated methylenes of the DMPC headgroup are not affected by adsorption of pentalysine on the PC/PS membranes. By contrast, the pentalysine produces significant changes in the quadrupolar splittings of the negatively charged DMPS headgroup. The results are discussed in relation to previous 2H NMR investigations of phospholipid headgroup perturbations arising from bilayer interaction with cationic molecules.

Deuterium↗
PubMed1988

Comparison of the central and peripheral effects of cetirizine and terfenadine.

The peripheral and central effects of 10 mg cetirizine 2 HCl and 60 mg terfenadine have been compared with placebo in 9 healthy male volunteers. The peripheral effect, in terms of cutaneous reactivity to 1 microgram histamine i.d., was measured by planimetry of the wheal and erythemas. Central effects were assessed with a self-evaluation visual scale and from the results of electroencephalographic spectrum analysis. Peripheral inhibition of histamine reactivity was more intense and quicker for cetirizine than for terfenadine. On the self-evaluation scale, no significant difference between terfenadine, cetirizine and placebo was noted. The quantified EEG did not show any variation in spectral parameters at any time after cetirizine. By contrast, at 6 h terfenadine had increased slow waves and had inhibited the alpha band. Thus, 10 mg cetirizine 2 HCl had less effect on the central nervous system than terfenadine 60 mg, whilst its peripheral action appeared more quickly and was more intense.

Adult↗
PubMed1988

Acyl chain orientational order in the hexagonal HII phase of phospholipid-water dispersions.

The deuterium nuclear magnetic resonance (2H NMR) spectrum of perdeuterated tetradecanol in a mixture of 1-palmitoyl-2-oleoyl-phosphatidylethanolamine (POPE) and water was used to compare the variation of the acyl chain orientational order parameter, S(n), with carbon position, n, in the liquid crystalline lamellar (L alpha) and hexagonal (HII) phases. The characteristics independence of S(n) with n (plateau) normally observed in the L alpha phase is replaced by a more rapid decrease of S(n) with n in the HII phase. It is suggested that as a consequence of the geometrical characteristics of the HII phase, there is an increase in conformational freedom available to different parts of the acyl chain.

Lipid Bilayers↗
PubMed1988

Effect of Carbolevure on intestinal fermentation induced by the ingestion of lactulose.

A double-blind trial involving two parallel groups of healthy volunteers was carried out in order to determine whether Carbolevure was capable of decreasing the over-production of intestinal gas induced by the ingestion of 15 ml of lactulose, a synthetic disaccharide not absorbed by the small intestine. Catabolism of this substrate by the anaerobic bacterial flora produces hydrogen, a constant fraction of which diffuses from the intestinal lumen into the blood, later to be excreted in expired air. Hydrogen levels were measured in air samples collected at the end of forced expiration. This hydrogen respiratory test was carried out before and after administration of Carbolevure to 17 volunteers or of a placebo to 15 volunteers, at a dose of three capsules morning and evening for seven days. Comparison of measurements of expired hydrogen by the subjects before and after administration showed a decrease in both groups. However, this decrease was statistically significant only in the group of volunteers having received Carbolevure.

Administration, Oral↗
PubMed1987

A comparison of the chemical analyses of cell lipids with their complete proton NMR spectrum.

Whole cells are made up of molecules in different environments to which NMR spectroscopy is sensitive. In particular, malignant and transformed cells contain lipids not only in bilayers but in isotropically tumbling domains which give rise to high-resolution spectra. We have recently developed a technique for simultaneously analyzing broadline and high-resolution signals (M. Bloom, K. T. Holmes, C. E. Mountford, and P. G. Williams, J. Magn. Reson., in press) and we report here its application to a range of rat, mouse, and human cell lines. Some selected features of the NMR spectra were compared with the chemical analysis of the whole-cell lipid. We found that in general the proportion of protons in the narrow methylene resonance at 1.3 ppm increased with the neutral lipid content of the cells. This peak was chosen because its T2 relaxation behavior correlates with metastatic potential in a rat model system. This new technique could be applied to other high-resolution components both in healthy and in diseased states.

Animals↗
PubMed1987

Regulation of starch synthesis: enzymological and genetic studies.

Significant advances have been made with respect to elucidating the structure, the allosteric site, interactions of effectors, covalent modifications, and the amino acid sequence of the ADPG synthetase. It is hoped that in the near future, sufficient information will be obtained to enable facile manipulation of the plant tissue ADPG synthetase gene and its product.

Allosteric Site↗
PubMed1986

Deuterium nuclear magnetic resonance investigation of the exchangeable sites on gramicidin A and gramicidin S in multilamellar vesicles of dipalmitoylphosphatidylcholine.

Solid gramicidin A and S and their interaction with DPPC bilayers were examined by 2H NMR as well as 31P NMR and differential scanning calorimetry (DSC). The deuterium spectra arose from deuterons associated with the peptide through chemical exchange in 2H2O. The spectra from both peptides were characterized by a quadrupolar splitting parameter, omega Q/2 pi approximately 150 kHz, and an asymmetry parameter, eta approximately 0.17. An additional 33 kHz, eta = 0 component arising from deuterons on mobile ornithine side chains was present in gramicidin S. In the gel phase of dipalmitoylphosphatidylcholine liposomes the gramicidins gave spectra that had components identical with those obtained from the solids. In the liquid-crystalline phase gramicidin A containing samples gave multicomponent spectra with a maximum quadrupolar splitting value of 133 kHz, eta = 0. A minimum in the T2e was observed, coinciding with the onset of the broadened phase transition measured by DSC and 31P NMR, due to the onset of axial rotation of the peptide in the bilayer. The different powder patterns in the liquid-crystalline spectra from gramicidin A probably arise from different amide sites along the transmembrane channel. The broad component of the 2H NMR spectra from gramicidin S in liposome preparations was not affected by the lipid-phase transition. The T2e was also constant over this temperature range. The results are consistent with a location of gramicidin S at the membrane surface.

Calorimetry, Differential Scanning↗
PubMed1986

Interaction of cytochrome c with mixed dimyristoylphosphatidylcholine-dimyristoylphosphatidylserine bilayers: a deuterium nuclear magnetic resonance study.

Deuterium nuclear magnetic resonance (2H NMR) was used to study the interaction of cytochrome c (from horse heart) with bilayers of mixed dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylserine (DMPS). Three types of labeled lipids were used: chain-perdeuterated phosphatidylcholine (DMPC-d54), chain-perdeuterated phosphatidylserine (DMPS-d54), and phosphatidylserine labeled at the alpha-position of the head group (DMPS-d2). Liposomes containing equimolar mixtures of DMPC and DMPS were found to bind cytochrome c with a maximum ratio of about 1 mg of cytochrome c per 1 mg of DMPS. The 2H NMR spectra of equimolar mixtures of DMPC-d54-DMPS and DMPC-DMPS-d54 were examined with and without cytochrome c. No change of the NMR spectra of either DMPC or DMPS could be detected after protein addition, for temperatures both above and below the phospholipid phase transition region. On the other hand, in the liquid-crystalline state, the transverse relaxation time, T2e, was reduced by 30-40% after protein addition. Measurements of the spin-lattice relaxation time, T1, showed, under all circumstances, multiple components. For simplicity, we have examined the shape of the relaxation curves at short and long times. Addition of protein increased by 2-fold the value of the slow T1 component of DMPS-d54 but not that of DMPC-d54. Partially relaxed spectroscopy allowed us to assign this slow component (at least in part) to the methyl group and C2H2 groups near the methyl end of the chains, i.e., far from the binding sites of the extrinsic protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

In vitro effect of the Escherichia coli heat shock regulatory protein on expression of heat shock genes.

In Escherichia coli, the ability to elicit a heat shock response depends on the htpR gene product. Previous work has shown that the HtpR protein serves as a sigma factor (sigma 32) for RNA polymerase that specifically recognizes heat shock promoters (A.D. Grossman, J.W. Erickson, and C.A. Gross Cell 38:383-390, 1984). In the present study we showed that sigma 32 synthesized in vitro could stimulate the expression of heat shock genes. The in vitro-synthesized sigma 32 was found to be associated with RNA polymerase. In vivo-synthesized sigma 32 was also associated with RNA polymerase, and this polymerase (E sigma 32) could be isolated free of the standard polymerase (E sigma 70). E sigma 32 was more active than E sigma 70 with heat shock genes; however, non-heat-shock genes were not transcribed by E sigma 32. The in vitro expression of the htpR gene required E sigma 70 but did not require E sigma 32.

Chromatography, Gel↗
PubMed1985

Dynamic properties of the backbone of an integral membrane polypeptide measured by 2H-NMR.

The 2H-NMR spectrum of the exchangeable hydrogens of the synthetic amphiphilic polypeptide, lys2-gly-leu24-lys2-ala-amide, was measured for the solid peptide at room temperature and, as a function of temperature, for the peptide incorporated into hydrated dipalmitoylphosphatidylcholine (DPPC) bilayers. This study is a prototype of a similar class of experiments which can be carried out on integral membrane proteins to characterize, quantitatively, the dynamic properties of integral membrane proteins. At temperatures below the DPPC gel-liquid crystalline phase transition, the 2H NMR spectrum was very similar to that of the solid peptide indicating that the peptide was immobilized in the lipid bilayer on the time scale (approximately equal to 10(-5) s) of the 2H-NMR measurements. The 2H-NMR spectrum above the phase transition corresponded to that expected from a peptide in the alpha-helical conformation reorienting rapidly about the symmetry axis of the alpha-helix. Measurements of the quadrupolar echo relaxation time, T2e, gave a quantitative measure of the correlation time, tau c, for this motion. The value of tau c decreased rapidly with increasing temperature as the fraction of DPPC molecules in the liquid crystalline phase increased, reaching a value of 2 X 10(-7) s above the phase transition. The observation of a characteristic minimum in T2e as the temperature was raised provided a definitive, quantitative interpretation of the T2e measurements. Using the known geometry of the peptide and the theory of uniaxial rotational diffusion, a value of eta = 1.1 poise was obtained for the effective viscosity of the membrane in close agreement with values obtained previously from transient linear dichroism measurements.

Calorimetry, Differential Scanning↗
PubMed1984

NMR methods for characterizing the state of the surfaces of complex mammalian cells.

It is shown that narrow 1H NMR resonances may be observed in cancer cells, and that these belong to fatty acyl chains of membrane lipids. A variety of NMR techniques such as Gaussian-Lorentzian deconvolution, and T1 and T2 measurements, may be used to subdivide these resonances further. The results of these various methods require that in the membrane structures the observed lipids tumble isotropically and sufficiently rapidly to give motionally narrowed 1H NMR lines.

Animals↗
PubMed1984

Mattress model of lipid-protein interactions in membranes.

A thermodynamic model is proposed for describing phase diagrams of mixtures of lipid bilayers and amphiphilic proteins or polypeptides in water solution. The basic geometrical variables of the model are the thickness of the hydrophobic region of the lipid bilayer and the length of the hydrophobic region of the proteins. The model incorporates the elastic properties of the lipid bilayer and the proteins, as well as indirect and direct lipid-protein interactions expressed in terms of the geometrical variables. The concept of mismatch of the hydrophobic regions of the lipids and proteins is an important ingredient of the model. The general phase behavior is calculated using simple real solution theory. The phase behavior turns out to be quite rich and is used to discuss previous experiments on planar aggregations of proteins in phospholipid bilayers and to propose a systematic study of synthetic amphiphilic polypeptides in bilayers of different thicknesses. The model is used to interpret the influence of the lipid-protein interaction on calorimetric measurements and on local orientational order as determined by deuterium nuclear magnetic resonance.

Lipid Bilayers↗
PubMed1984

Acute embolic bilateral renal artery occlusions in an elderly patient--case report: importance of early diagnosis.

Acute bilateral renal artery occlusion by emboli is a rare event and diagnosis is very often delayed. There is a high mortality rate because of anuria and controversy exists concerning an appropriate therapeutic regimen. We present the case of an elderly patient with bilateral artery occlusion, treated conservatively with anticoagulants, fibrinolytic agents and dialysis, and a review of the pertinent literature.

Acute Disease↗