2,813 research outputs found
An investigation into the mechanism of action of Amphiphilies with Antineoplastic properties
No full textA range of type I amphiphiles with molecular shape analogues to cytotoxic ether lipids like HDPC and ET-18-OMe were synthesised. These compounds were quaternary ammonium, polyethylene glycol and phosphate ester amphiphiles. Quaternary ammonium amphiphiles were synthesised by the Menschutkin reaction. Polyethylene glycol amphiphiles were synthesised using a phase transfer Williamson reaction developed in this study. Phosphate ester amphiphiles were synthesised from the reaction of halophosphates alcohols. Each compound was tested for cytotoxic activity against the HL-60 cell line and a structure activity series was compiled. A correlation between increasing cytotoxic activity and increasing type I molecular shape was observed. Investigation of the aggregate properties of the type I amphiphiles showed that detergency was not a viable mechanism of action at the ED50 concentration. A physico-chemico model for the mechanism of action of type I amphiphiles was investigated. Testing a hypothesis where type I amphiphiles are thought to modulate the stored elastic stress of cell membranes, preventing translocation of the CCT enzyme. Inhibiting CDP-choline synthesis and bulk de novo PC biosynthesis resulting in cell death through apoptosis. Electrospray Mass Spectrometry was used to determine the composition of endogenous PC, PE and newly synthesised PC phospholipid fractions of both whole cells and nuclei. After incubation with type I amphiphiles decreases in total new PC synthesis were observed. Increases in the synthesis of type II phospholipids in the phospholipid fractions were also observed as predicted by the physico-chemico model under test.</p
Cationic type I amphiphiles as modulators of membrane curvature elastic stress in vivo
No full textRecently we proposed that the antineoplastic properties observed in vivo for alkyl-lysophospholipid and alkylphosphocholine analogues are a direct consequence of the reduction of membrane stored elastic stress induced by these amphiphiles. Here we report similar behavior for a wide range of cationic surfactant analogues. Our systematic structure?activity studies show that the cytotoxic properties of cationic surfactants follow the same pattern of activity we observed previously for alkyl-lysophospholipid analogues, indicating a common mechanism of action that is consistent with the theory that these amphiphiles reduce membrane stored elastic stress. We note that several of the cationic surfactant compounds we have evaluated are also potent antibacterial and antifungal agents. The similarity of structure?activity relationships for cationic surfactants against microorganisms and those we have observed in eukaryotic cell lines leads us to suggest the possibility that the antibacterial and antifungal properties of cationic surfactants may also be due to modulation of membrane stored elastic stress
Testing the hypothesis that amphiphilic antineoplastic lipid analogues act through reduction of membrane curvature elastic stress
No full textThe alkyllysophospholipid (ALP) analogues Mitelfosine and Edelfosine are anticancer drugs whose mode of action is still the subject of debate. It is agreed that the primary interaction of these compounds is with cellular membranes. Furthermore, the membrane-associated protein CTP: phosphocholine cytidylyltransferase (CCT) has been proposed as the critical target. We present the evaluation of our hypothesis that ALP analogues disrupt membrane curvature elastic stress and inhibit membrane-associated protein activity (e.g. CCT), ultimately resulting in apoptosis. This hypothesis was tested by evaluating structure-activity relationships of ALPs from the literature. In addition we characterized the lipid typology, cytotoxicity and critical micelle concentration of novel ALP analogues that we synthesized. Overall we find the literature data and our experimental data provide excellent support for the hypothesis, which predicts that the most potent ALP analogues will be type I lipids
The effect of lipids on the enzymatic activity of 6-phosphofructo-1-kinase from B. stearothermophilus
No full text6-Phosphofructo-1-kinase (PFK-1), a major regulatory enzyme in the glycolysis pathway, is a cytoplasmic enzyme with complicated allosteric kinetics. Here we investigate the effects of lipids on the activity of PFK from Bacillus stearothermophilus (BsPFK), to determine whether BsPFK shares any of the membrane binding or lipid binding properties reported for some mammalian PFKs. Our results show that large unilamellar vesicles (LUVs) composed of either the phospholipid 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) or of 1:1 (mole ratio) DOPC and the fatty acid, oleic acid (OA), cause a three-fold increase in Vmax, depending on the lipid concentration and vesicle composition, but no change in Km. Further studies show lipids do not reverse the allosteric inhibitory effects of phosphoenolpyruvate (PEP) on BsPFK. SDS/PAGE studies do not show significant binding of the BsPFK tetramer to the surface of the phospholipid vesicles, suggesting that modulation of catalytic activity is due to binding of lipid monomers. By simulating the kinetics of BsPFK interaction with vesicles and lipid monomers we conclude that the change in BsPFK catalytic activity with respect to lipid concentration is consistent with monomer abstraction from vesicles rather than direct uptake of lipid monomers from solution
Effect of membrane lipids on phosphofructokinase from Bacillus stearothermophilus using a novel 33P radiochemical assay
No full textPhosphofructokinase (PFK-1), a major regulatory enzyme of glycolysis, catalyses the phosphorylation of d-fructose 6-phosphate by ATP to yield d-fructose 1,6-bisphosphate. Mammalian PFK-1 is known to bind to biomembranes with a regulatory effect on enzyme activity (Karadsheh and Uyeda, 1977). We have conducted a study into whether PFK-1 activity depends on membrane lipid composition and whether this enzyme is regulated via membrane stored curvature elastic stress, in an analogous manner to CTP:phosphocholine cytidylytransferase (CCT) (Attard et al., 2000 G.S. Attard, R.H. Templer, W.S. Smith, A.N. Hunt and S. Jackowski, PNAS 97 (16) (2000), p. 9032. Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (82)[Attard et al., 2000] and [Attard et al., 2006]). As part of this investigation, we developed a novel 33P radiochemical assay for PFK-1. The assay combines the benefits of a previously available 32P assay (Sola-Penna et al., 2002), with the advantage of a markedly smaller decay energy. Kinetic studies yielded comparable results to both the spectrophotometric and 32P radiochemical assays, confirming the reliability of the method. The effect of vesicles composed of dioleoyl phosphatidylcholine (DOPC) and oleic acid (OA) on PFK-1 from Bacillus stearothermophilus was studied. OA was found to increase catalytic activity twofold and threefold compared to DOPC and no lipid present, respectively. While these results suggest that stored curvature elastic energy may play a role in modulating enzyme activity, they are significantly different from the results obtained with CCT. Therefore, interesting questions arise about the fundamental mechanisms that underlie the effect of membrane lipid composition on PFK-1 activity
Marcus Joseph Wright memoirs, MSS.1585
No full textAbstract: An incomplete typescript copy (18 pp.) of, "Memoirs of Brigadier General Marcus J. Wright, CSA."Scope and Content Note: The collection contains an incomplete typescript copy (18 pp.) of, "Memoirs of Brigadier General Marcus J. Wright, CSA," which includes a family genealogy, and accounts of his early life in Tennessee and his career.Biographical/Historical Note: Confederate General and author from Tennessee
Marcus on Belief and Belief in the Impossible
Full text linkI review but don’t endorse Marcus’ arguments that impossible beliefs are impossible. I defend her claim that belief’s objects are, in some important sense, not the bearers of truth and falsity, discuss her dispositionalism about belief, and argue it’s a good fit with the idea that belief’s objects are Russellian states of affairs.
Reviso, pero no suscribo, los argumentos de Marcus a favor de que las creencias imposibles son imposibles.
Defiendo su tesis de que los objetos de las creencias no son, en algún sentido importante, los soportes
de la verdad y la falsedad; discuto su disposicionalismo acerca de las creencias y argumento que encaja bien
con la idea de que los objetos de las creencias son estados de cosas russellianos
Formation of inverse topology lyotropic phases in dioleoylphosphatidylcholine/oleic acid and dioleoylphosphatidylethanolamine/oleic acid binary mixtures
No full textThe addition of saturated fatty acids (FA) to phosphatidylcholine lipids (PC) that have saturated acyl chains has been shown to promote the formation of lyotropic liquid-crystalline phases with negative mean curvature. PC/FA mixtures may exhibit inverse bicontinuous cubic phases (Im3m, Pn3m) or inverse topology hexagonal phases (H-II), depending on the length of the acyl chains/fatty acid. Here we report a detailed study of the phase behavior of binary mixtures of dioleoylphosphatidylcholine (DOPC)/oleic acid (OA) and dioleoylphosphatidylethanolamine (DOPE)/oleic acid at limiting hydration, constructed using small-angle X-ray diffraction (SAXD) data. The phase diagrams of both systems show a succession of phases with increasing negative mean curvature with increasing OA content. At high OA concentrations, we have observed the occurrence of an inverse micellar Fd3m phase in both systems. Hitherto, this phase had not been reported for phosphatidylethanolamine/fatty acid mixtures, and as such it highlights an additional route through which fatty acids may increase the propensity of bilayer lipid membranes to curve. We also propose a method that uses the temperature dependence of the lattice parameters of the H-II phases to estimate the spontaneous radii of curvature (R-0) of the binary mixtures and of the component lipids. Using this method, we calculated the R-0 values of the complexes comprising one phospholipid molecule and two fatty acid molecules, which have been postulated to drive the formation of inverse phases in PL/FA mixtures. These are -1.8 nm (+/-0.4 nm) for DOPC(OA)(2) and -1.1 nm (+/-0.1 nm) for DOPE(OA)(2). R-0 values estimated in this way allow the quantification of the contribution that different lipid species make to membrane curvature elastic properties and hence of their effect on the function of membrane-bound proteins
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