1
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Abstract
The dispersity, size, and self-interaction of generation 5 polyamidoamine dendrimeric polymers with different terminal groups (surfaces) were characterized using several physicochemical techniques. Amino-surface dendrimers form oligomeric aggregates in aqueous solution, even in the presence of high salt concentrations (0.6M sodium phosphate). In contrast, the hydroxyl-surface polymer G5-OH behaves as a single homogeneous (or paucidisperse) species at low concentration. Measurements of density increment and the sedimentation and diffusion coefficients of G5-OH suggest a more swollen, porous structure than a globular protein of comparable mass. Measurements of the concentration dependence of sedimentation equilibrium of G5-OH in pH 7.2 phosphate buffer indicate the presence of significant electrostatic repulsion overlaid on weakly attractive interactions, leading to the formation of nonspecific aggregates at sufficiently high dendrimer concentration.
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Affiliation(s)
- A Nourse
- Section on Physical Biochemistry, Laboratory of Biochemistry and Genetics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda MD 20892-0830, USA
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2
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Schuck P, Millar DB, Kortt AA. Determination of binding constants by equilibrium titration with circulating sample in a surface plasmon resonance biosensor. Anal Biochem 1998; 265:79-91. [PMID: 9866711 DOI: 10.1006/abio.1998.2872] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
A commercial surface plasmon resonance biosensor, BIACORE X, is employed as a detector in a closed loop of a small sample volume. The sample is continuously circulated by an external syringe pump over two sensor spots, one functionalized with immobilized binding sites to a soluble binding partner in the mobile phase and one serving as a reference surface. A binding isotherm for the interacting macromolecules can be obtained by a stepwise titration of the soluble reactant into the circulating loop, each step followed by observation of the signal increase until equilibrium is attained. Binding constants can be measured under conditions free of mass transport artifacts and without the requirement for regeneration of the immobilized binding sites. This procedure is similar to the stepwise titration procedure described for the cuvette-based sensor design (D. R. Hall and D. J. Winzor, 1997, Anal. Biochem. 244, 152-160). In the presented configuration, the high baseline stability of the instrument combined with the availability of a reference surface for the detection of nonspecific binding permits refractive index changes upon addition of the aliquots to be measured, as well as accounting for temperature or instrumental drifts, and allows for a very long experimental time. This feature extends the applicability of equilibrium titration to systems with higher affinity or slower dissociation rate constants. Furthermore a solution competition titration is described that avoids artifacts from the immobilization procedure to provide a method for measurement of binding constants in solution. Kinetic information on the complex dissociation can also be obtained by combination of sample delivery via the external pump with the injection of competitor via the microfluidics of the biosensor. The rapid injection of high concentrations of competitor allows the observation of fast dissociation processes under conditions minimizing rebinding.
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Affiliation(s)
- P Schuck
- Molecular Interactions Resource, Bioengineering and Physical Science Program, ORS, National Institutes of Health, Bethesda, Maryland 20892, USA.
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3
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Millar DB. Negative cooperativity in tryptophan synthase alpha subunit dissociation is caused by the bound coenzyme: pyridoxal 5'-phosphate. Anal Biochem 1998; 264:271-8. [PMID: 9866693 DOI: 10.1006/abio.1998.2840] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Sedimentation equilibrium studies of dilute solutions of tryptophan synthase reveal dissociation from the holoenzyme form, alpha 2 beta 2, into mixtures of alpha beta 2, small amounts of beta 2, and alpha as well as the original alpha 2 beta 2 holoenzyme. The holoenzyme form is stabilized by pyridoxal 5'-phosphate. A new sedimentation equilibrium analytical procedure shows the dissociation of the second alpha subunit to be negatively cooperative. The analytical procedure calculates theoretical error profiles with assumed values of the dissociation constant, k, and a cooperativity parameter until a match is made between one of the theoretical profiles and that computed from experimental data. The latter profile is calculated with an experimentally determined k and assumed values of the cooperativity parameter.
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Affiliation(s)
- D B Millar
- New Ideas Company, Rockville, Maryland 20852, USA
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4
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Abstract
A new method is described that allows measurement of the molar mass of the solute within 15 to 30 min after start of a conventional long-column sedimentation equilibrium experiment. A series of scans of the concentration distribution in close vicinity of the meniscus, taken in rapid succession after the start of the centrifuge run, is analyzed by direct fitting using the Lamm equation and the Svedberg equation. In case of a single solute, this analysis of the initial depletion at the meniscus reveals its buoyant molar mass and sedimentation coefficient with an accuracy of approximately 10% and provides gross information about sample heterogeneity. This method can be used to study macromolecules that do not possess the prolonged stability needed in conventional sedimentation equilibrium experiments and it can increase the efficiency of sedimentation equilibrium experiments of previously uncharacterized samples.
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Affiliation(s)
- P Schuck
- Molecular Interactions Resource, BEPS, OD, National Institutes of Health, Bethesda, Maryland 20892, USA.
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5
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Abstract
Pelleting and resuspension of Fura 2-labeled c6 glioma cells leads to a large Ca flux characterized by a high initial internal level of Ca which rapidly declines to close to basal levels. The effect has been termed resuspension-induced ion flux (RIIF). The RIIF effect is temperature dependent and requires external calcium, cytoskeletal integrity, and functional calcium and potassium channels. The magnitude of the RIIF effect is dependent upon pelleting speed, suggesting cell contact and reduction in external fluid medium to be important causative parameters. Several other cell species also exhibit the RIIF effect.
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Affiliation(s)
- D B Millar
- New Ideas, Co., Rockville, Maryland 20852, USA
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6
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Darawshe S, Millar DB, Ahmed SA, Miles EW, Minton AP. Dissociation equilibria of the tryptophan synthase alpha 2 beta 2 complex in saline buffer and guanidine isothiocyanate, as studied by sedimentation equilibrium. Biophys Chem 1997; 69:53-62. [PMID: 9440208 DOI: 10.1016/s0301-4622(97)00078-1] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The dissociation equilibria of Salmonella typhimurium tryptophan synthase alpha 2 beta 2 complex were studied via centrifugation of the complex to sedimentation equilibrium in neutral saline buffers containing 0 to 137 mM guanidine isothiocyanate (GuSCN). The resulting concentration gradients were analyzed in the context of an equilibrium model for sequential dissociation of two alpha subunits from a stable beta 2 subunit. Under the conditions of these experiments, the first dissociation constant alone could be evaluated at GuSCN concentrations < or = 100 mM, and the second dissociation constant alone could be evaluated at GuSCN = 137 mM. At intermediate GuSCN, both dissociation constants were sufficiently well defined to rule out the presence of a large equilibrium cooperative effect in the stepwise dissociation of the alpha subunits.
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Affiliation(s)
- S Darawshe
- Section on Physical Biochemistry, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892-0830, USA
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7
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Abstract
Beta-endorphin and naloxone bind to Jurkat cell membrane preparations and can mutually displace each other from membrane binding sites. Tetraethylammonium ion, a potassium channel blocker, competitively displaces beta-endorphin and naloxone from membrane binding sites. Mitogen stimulated calcium ion flux is inhibited by tetraethyl ammonium and this inhibition is relieved by naloxone. With data derived from whole cell calcium ion flux studies, we accurately calculated the competitive displacement of beta-endorphin and naloxone from membrane preparations by tetraethylammonium thus showing that the action of these agents on potassium channels does not require second messengers. Using the resuspension induced ion flux technique, we find that beta-endorphin competes against naloxone for binding to Jurkat cells and naloxone competes against charybdotoxin, a potassium channel inhibitor, which like tetraethylammonium, is known to bind to the outer vestibule of the channel. Patch clamp electrophysiological studies show that beta-endorphin and naloxone exert complex actions on potassium channels in the presence or absence of mitogens. We conclude that one molecule of beta-endorphin or naloxone, but not both at the same time, bind to an area near the charybdotoxin/tetraethylammonium binding locus of Jurkat potassium channels.
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8
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Abstract
10(-6) M n-formyl-methionyl-leucyl-phenylalanine (FMLP) stimulated Ca2+ flux in human neutrophils is characterized by a profile composed of two peaks of different amplitude and breadth. beta-Endorphin inhibited the magnitude and modulated the kinetics of the second peak in a manner which was dose-dependent and could reflect either negative cooperativity or heterogeneity of binding sites. The second peak arises from calcium channel activity since in the presence of nifedipine or EGTA it was not evident while the first peak was reduced about 24%. Similarly, at 15 degrees C, where we were unable to detect any channel activity, the first peak was diminished by 35% and beta-endorphin had no detectable effect on this peak. These results led us to conclude that the first peak is chiefly composed of Ca2+ recruited from cytosolic stores which are relatively insensitive to the above treatments and a smaller fraction of calcium originating in calcium channel activity. Hence, we reason that beta-endorphin modulates only the calcium ion flux arising from calcium channel function.
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9
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Abstract
Natural killer (NK) cell activity and mitogen-stimulated spleenocyte proliferation were measured in rats exposed to stress in the form of avoidable and unavoidable shock. Rats that could avoid shock exhibited higher NK activity than either unshocked controls or rats that could not avoid shock. The latter were yoked to the avoidance rats and thus received the same number and frequency of shocks as did the avoidance group. The increased NK activity in the avoidance group appears due to a higher number of NK cells in this group as compared with those in the control or unavoidable shock groups. Additionally, NK activity was found to be proportional to avoidance response rate, with a majority of animals exceeding the minimal temporal avoidance requirement. Mitogen-stimulated proliferation of spleenocytes was also increased several fold in the group that could avoid shock as compared with that which could not and controls. The difference in NK activity and mitogen-stimulated proliferation could not be ascribed to differences in cortisol levels. The results indicate that behavior which results in the avoidance of aversive stimuli can lead to significant enhancement of immune system competence.
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Affiliation(s)
- D B Millar
- Neuropsychiatry Branch, National Institutes of Mental Health Neurosciences Center, Washington, DC 20032
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10
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Millar DB. Fluorstamp. Biotechniques 1993; 14:764. [PMID: 8512698] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Affiliation(s)
- D B Millar
- Neuropsychiatry Branch, National Institute of Mental Health Neurosciences Center, St. Elizabeths, Washington, DC 20032
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11
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Abstract
We find that beta-endorphin (Bend) can have, positive, negative, or neutral dose-dependent effects on the mitogen-stimulated proliferation of human peripheral blood lymphocytes. The distribution of positive, negative, or neutral responses was nonrandom. In studies carried out over a year, we show that an individual's mitogen-stimulated lymphocyte proliferative response to Bend can change with time. We show that the inhibition induced by cortisol can be, in part, relieved by Bend. On the basis of our results and those of others in the field, we put forward a model that can qualitatively account for many of the observations we and other investigators have made.
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Affiliation(s)
- D B Millar
- Laboratory of Biochemical Genetics, National Institute of Mental Health Neuroscience Center at St. Elizabeths, Washington, D.C. 20032
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12
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Hough CJ, Halperin JI, Mazorow DL, Yeandle SL, Millar DB. Beta-endorphin modulates T-cell intracellular calcium flux and c-myc expression via a potassium channel. J Neuroimmunol 1990; 27:163-71. [PMID: 2139666 DOI: 10.1016/0165-5728(90)90066-v] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
To characterize the effect of beta-endorphin on T-lymphocyte activation, we examined its influence on membrane currents, intracellular calcium flux, and c-myc mRNA levels during mitogenic stimulation of Jurkat cells. While beta-endorphin weakly enhanced voltage-activated K+ currents of Jurkat cells by itself, it suppressed these currents in the presence of mitogen. Naloxone, by itself, also enhanced K+ current amplitude, but in the presence of mitogen partially reversed the suppressive effect of beta-endorphin. A 5-30 min exposure to beta-endorphin resulted in an increase in the rate of mitogen-stimulated intracellular calcium release and an increase in c-myc mRNA levels relative to controls. Longer exposure (1-2 h) to beta-endorphin retarded intracellular calcium release, and suppressed c-myc expression. The suppressive effects were reversed by naloxone and mimicked by the K+ channel blocker, tetraethylammonium ion. These data suggest that opiate receptors and K+ channels of Jurkat cells are functionally coupled in a way that modulates intracellular calcium release and c-myc expression - two key processes in T-cell mitogenesis.
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Affiliation(s)
- C J Hough
- Laboratory of Biochemical Genetics, NIMH, Neuroscience Center, St. Elizabeths, Washington, DC 20032
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13
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Abstract
Several fluorescent probes have been used in the past to monitor and to measure intracellular calcium and calcium fluxes. The most widely used of these probes are those developed by Tsien. We address the markedly different values obtained when comparing Quin-2 (the original probe) with Fura-2 (a second-generation probe). In most cases the values for intracellular calcium have been considered to be interchangeable for the different probes. Using several different hematopoietic cell lines we show that in no case do the two probes yield equivalent values.
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Affiliation(s)
- D L Mazorow
- Immunobiology and Transplantation Department, Naval Medical Research Institute, Bethesda, Maryland 20814
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14
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Simpkins CO, Mazorow DL, Alailima ST, Tate EA, Sweatt W, Johnson M, Shariff K, Millar DB. Prostaglandin D2 modulates human neutrophil intracellular calcium flux and inhibits superoxide release via its ring carbonyl. Life Sci 1990; 46:793-801. [PMID: 2319907 DOI: 10.1016/0024-3205(90)90067-2] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
We compared the effects of prostaglandin D2 (PGD2), prostaglandin F2 alpha (PGF2) and various ketones on superoxide (OX) release by human neutrophils, which had been stimulated by N-formyl methionyl leucyl phenylalanine (FMLP). Our data suggested that the ring carbonyl of PGD2 is essential to its inhibitory effect on OX release, but the carbonyl group as a ketone, alone is not sufficient. Using the fluorescent Ca2+ probe, Fura-2AM, we found that PGD2 increased the rate of decline of FMLP stimulated intracellular free Ca2+ (Ca)i, but that PGF2 had no effect. cAMP altered FMLP stimulated (Ca)i, in a pattern similar to PGD2. Furthermore, the ring carbonyl of PGD2 is crucial to its effect on OX as well as on (Ca)i.
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Affiliation(s)
- C O Simpkins
- Naval Medical Research Institute, Bethesda, Maryland 20814-5055
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15
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Simpkins CO, Chenet BP, Kang YH, Mazorow DL, Millar DB, Hollis VW. Human erythrocytes have binding sites for beta-endorphin. J Natl Med Assoc 1989; 81:1149-53. [PMID: 2560064 PMCID: PMC2626097] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Monoiodinated human beta-endorphin was found to bind specifically to human erythrocytes. Unlabeled beta-endorphin and beta-endorphin inhibited binding, but (-)naloxone, [D-Ala2, D-Leu5]-enkephalin, and leu- and met-enkephalin did not. Immunoelectron microscopy, using rabbit anti-beta-endorphin antibody, an antirabbit IgG secondary antibody, and complexed horseradish peroxidase, revealed that at low concentrations beta-endorphin binds to the cell surface. Electron spin resonance spectroscopy showed no effect of beta-endorphin on membrane fluidity. This receptor does not appear to conform to the characteristics of an opiate receptor.
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16
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Millar DB. A safe and efficient method of loading radiolabeled probe into blotting bags. Biotechniques 1989; 7:936. [PMID: 2698667] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Affiliation(s)
- D B Millar
- Laboratory of Biochemical Genetics, NIMH, Neuroscience Center at St. Elizabeths, Washington, D.C. 20032
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17
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Millar DB. An inexpensive storage box for 0.5 and 1.5 ml microcentrifuge/test tubes. Biotechniques 1989; 7:32. [PMID: 2629831] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Affiliation(s)
- D B Millar
- Immunology & Transplantation Department, Naval Medical Research Institute, Bethesda, MD 20814
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18
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Quesada MH, Millar DB, Smejkal R. Tubulin synthesis in the regenerating rat superior cervical ganglion: a biphasic response. J Neurobiol 1986; 17:77-82. [PMID: 3701325 DOI: 10.1002/neu.480170203] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Axotomy of a major cranial post ganglionic branch of the superior cervical ganglion of an adult rat resulted in increased radiolabeling of tubulin and microtubule-associated proteins after an in vitro 5-h incubation with [14C]-methionine. The increased incorporation of the radiolabel began at day 1 postoperatively and exhibited a biphasic response, peaking at days 3 and 8.
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19
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Abstract
Exposure of microtubular protein to ultraviolet light inhibits its assembly into morphologically normal microtubules. This effect appeared to result primarily from damage to the tubulin dimers. The damage consisted of a conformational change, a loss of two free sulfhydryl groups, a production of higher molecular weight cross-linked species, and the formation of aggregated amorphous material upon polymerization.
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20
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Millar DB, Christopher JP, Hunter J, Yeandle SS. The effect of exposure of acetylcholinesterase to 2,450-MHz microwave radiation. Bioelectromagnetics 1984; 5:165-72. [PMID: 6732873 DOI: 10.1002/bem.2250050205] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
The effect of 2,450-MHz pulsed microwave radiation on the enzyme activity of membrane-free acetylcholinesterase was studied while the enzyme was in the microwave field. We found no significant effect of microwave radiation on enzyme activity using a wide variety of power densities, pulse widths, repetition rates, and duty cycles. This suggests that simple, direct modification by microwave energy of acetylcholinesterase structure and enzymic activity is not related to microwave alteration of acetylcholinesterase central nervous system levels.
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21
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Abstract
The dimensions of the small intestinal diffusion barrier interposed between luminal nutrients and their membrane receptors were determined from kinetic analysis of substrate hydrolysis by integral surface membrane enzymes. The calculated equivalent thickness of the unstirred water layer was too large to be compatible with the known dimensions of rat intestine. The discrepancy could be reconciled by consideration of the mucous coat overlying the intestinal surface membrane. Integral surface membrane proteins could not be labeled by an iodine-125 probe unless the surface coat was first removed. The mucoprotein surface coat appears to constitute an important diffusion barrier for nutrients seeking their digestive and transport sites on the outer intestinal membrane.
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22
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Abstract
Ultraviolet irradiation of 11S acetylcholinesterase (acetylcholine acetylhydrolase, EC 3.1.1.7) produces a loss of tryptophan fluorescence which is best described as the sum of two separable first-order processes, one much more rapid than the other. In addition, the enzyme undergoes an all-or-none inactivation that is monotonically first order. Simultaneous with activity loss, photoscission takes place and results in a molecular weight drop of 1 x 10(5); this decrease is first order with a rate constant identical to that for enzymatic inactivation. These processes are accompanied by apparent conformational changes, as shown by circular dichroic and difference absorption spectra. The relative photochemical inactivation efficiency of incident light is unity when corrected for the wavelength dependence of fluorescence excitation, which is consistent with an efficient Förster resonance transfer of energy among the aromatic chromophores. The extreme sensitivity of acetylcholinesterase to photodestruction upon photon absorption and the several events that follow it not only suggest that these findings might be a basis for a useful molecular probe of the structure of this enzyme, but also indicate that additional care should be taken when conducting spectroscopic studies in the UV region.
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23
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Himel CM, Taylor JL, Pape C, Millar DB, Christopher J, Kurlansik L. Acridine araphanes: a new class of probe molecules for biological systems. Science 1979; 205:1277-9. [PMID: 472743 DOI: 10.1126/science.472743] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The bis-acridine ring system forms the basis for new biophysical probes of novel stereochemistry. Spectral data indicate that certain alkylene bridged bis-9-aminoacridines have a parallel plane conformation of predictable interplane distance. The parallel plane conformation is independent of solvent and thus is different from nucleic acid systems. This stable conformation allows these compounds to be used as sensitive "rulers" for describing binding site geometry in cholinergic enzymes and in the delineation of the mechanism of allosteric control in acetylcholinesterase.
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24
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Abstract
At high detergent concentrations, approximately the equivalent of 2 micelles of TX-100 reversibly bind to acetylcholinesterase and fully inhibit the enzyme. This result suggests that the appropriate lipid environment might regulate this neuronal enzyme's function.
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25
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Abstract
Detergent binding studies indicated that the neural enzyme, acetylcholinesterase, did not exhibit the properties of an integral membrane protein. The 11S form was isolated by affinity chromatography from a tryptic digest and the 14S and 18S forms in like manner from an undigested preparation. Studies were performed with [3H]TX-100 to determine the extent of binding by these forms and with catalase and human low density lipoprotein as reference proteins. All forms of the enzyme bound less than 0.04 mg TX-100/mg protein which is only slightly higher than binding by catalase and about 25 fold lower than the binding exhibited by low density lipoprotein.
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27
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Abstract
11-S acetylcholinesterase (acetylcholine hydrolase, EC 3.1.1.7) purified by affinity chromatography of trypsin-digested homogenates was shown to be contaminated with three other active forms of enzyme. The initial purification used an affinity column of the inhibitor, N-methylacridinium ion. Chromatography of the "affinity-pure" sample on hydroxyapatite resulted in two peaks of acetylcholinesterase activity. One peak contained only a form sedimenting at 11-S (approx. 85% of the recovered activity). The other peak consisted of a 9.5-S form, in addition to 14-S and 18-S forms. The 9.5-S form (approx. 7% of the activity) co-electrophoresed with 11-S in 6% polyacrylamide gels and co-sedimented with the same form in sucrose density gradients containing 0.1 M NaCl. The purified 11-S enzyme was shown to be homogeneous by sucrose density gradient centrifugation and electrophoresis. These results indicate that 11-S acetylcholinesterase may be unsuitable for some characterization studies due to undetected contamination by the 9.5-S form.
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28
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Abstract
Chloroform/methanol rechromatography on Sephadex LH-20 of fractions isolated from organic solvent extracts of E. electricus electric organs exhibited alterations in elution point compared to the original chromatography. Additionally, 3H decamethonium bromide did not coelute with any of the observed fractions. It is concluded that as presently described the organic solvent isolation procedure for the cholinergic receptor exhibits undesirable characteristics.
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Kothari RM, Millar DB, Grafius MA, Christopher JP. Time dependent formation of acetylcholinesterase isozymes. Experientia 1978; 34:160-1. [PMID: 624339 DOI: 10.1007/bf01944650] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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30
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Baum BJ, Bird JL, Millar DB, Longton RW. Isolation and partial characterization of an histidine-rich polypeptide from parotid saliva of the monkey, Macaca nemestrina. Comp Biochem Physiol A Comp Physiol 1977; 56:115-20. [PMID: 11920 DOI: 10.1016/0300-9629(77)90171-2] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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32
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Abstract
Five spin-labeled 9-aminoacridines, each bearing either a 4-(2,2,6,6-tetramethyl-1-piperidinyloxy) or a 3-(2,2,5,5-tetramethyl-1-pyrrolidinyloxy) moiety in the 9 position, have been synthesized and assayed for biological activity in three different test systems. Sedimentation velocity measurements indicated that the labels caused unwinding of calf thymus DNA. Those acridines which contained both 6-chloro and 2-methoxy substituents were less toxic to leukemia L1210 in static culture than the corresponding unsubstituted analogues. While the unsubstituted aminoacridines were quite good inhibitors of Escherichia coli DNA-primed RNA polymerase, the 6-chloro-2-methoxy-substituted compounds stimulated this enzyme system. In the presence of E.coliDNA, the ESR spectrum of 4-[(6-chloro-2-methoxy-9-acridinyl)amino]-2,2,6,6-tetramethyl-1-piperidinyloxyl (12) became broad and highly asymmteric with a maximal hyperfine splitting of 57.5 G. This observation suggests that when 12 intercalates into DNA the piperidinyl moiety that bears the nitroxide group becomes highly immobilized. These results suggest that the spin-labeled 9-aminoacridines will be useful probes for nucleic acids.
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33
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Kothari RM, Grafius MA, Millar DB. A simple and rapid chromatographic method for the immobilization of acetylcholinesterase from electric eel. Anal Biochem 1976; 71:273-80. [PMID: 1275230 DOI: 10.1016/0003-2697(76)90036-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
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34
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Millar DB. Partial characterization of the 1-anilino-8-naphthalene sulfonate-adrenochrome semicarbazide interaction site in erythrocyte ghost membrane fragments. Biophys Chem 1975; 3:297-306. [PMID: 172164 DOI: 10.1016/0301-4622(75)80022-6] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The effect of adrenochrome semicarbazide on the conformation of erythrocyte ghost membranes has been studied by ANS fluorescence, lipid and sulfhydryl spin labels and circular dichroism. No large conformational alterations in the membrane were detected by these techniques. Noncompetitive quenching of ANS fluorescence by ADCS suggests ADCS to interact with the membrane at sites close to the ANS binding domain.
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35
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Abstract
Triton X-100 micelle formation at 25 degrees C was studied by use of sedimentation equilibrium and fluorescence spectroscopic techniques. The apparent molecular weight of the major Triton X-100 micelle was found to be 81250, indicating a micelle number of 125. A micelle number of 121 was obtained with fluorescence titration experiments, which showed one molecule of 1-anilino-8-naphthalene sulfonate binding per micelle with an apparent association constant of 0.9 x 10(5) M. The fluorescent titration experiments also indicated the presence of another TX-100 binding species of variable size.
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36
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Millar DB. The quaternary structure of lactate dehydrogenase. II. The mechanisms, kinetics and thermodynamics of dissociation, denaturation and hybridization in ethylene glycol. Biochim Biophys Acta 1974; 359:152-76. [PMID: 4367982 DOI: 10.1016/0005-2795(74)90140-8] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
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Abstract
There is a small but distinct difference in DNA base composition between the typhus and spotted fever groups of rickettsiae. The molar percentages of guanine plus cytosine for Rickettsia prowazeki, R. typhi, and R. canada are approximately 30, for R. rickettsi, R. conori, and R. akari they are about 32.5. The percentage for trench fever rickettsia, Rochalimaea quintana, is 38.6.
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Millar DB, Summers MR, Niziolek JA. Spontaneous in vitro hybridization of LDH homopolymers in the undenatured state. Nat New Biol 1971; 230:117-9. [PMID: 5279339 DOI: 10.1038/newbio230117a0] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
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Millar DB, Mackenzie M. The properties of the helix and coil forms of polyribouridylic acid and its halogenated analogs. Biochim Biophys Acta 1970; 204:82-90. [PMID: 5437678 DOI: 10.1016/0005-2787(70)90491-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
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Millar DB, Frattali V, Willick GE. The quaternary structure of lactate dehydrogenase. I. The subunit molecular weight and the reversible association at acid pH. Biochemistry 1969; 8:2416-21. [PMID: 5816379 DOI: 10.1021/bi00834a025] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
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Millar DB, Willick GE, Steiner RF, Frattali V. Soybean inhibitors. IV. The reversible self-association of a soybean proteinase inhibitor. J Biol Chem 1969; 244:281-4. [PMID: 5813008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
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Grafius MA, Friess SL, Millar DB. Analysis of the polydispersity of acetylcholinesterase by transport methods in the ultracentrifuge. Arch Biochem Biophys 1968; 126:707-21. [PMID: 5672525 DOI: 10.1016/0003-9861(68)90458-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
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