scholarly journals Diffusion in the aqueous compartment.

1984 ◽  
Vol 99 (1) ◽  
pp. 180s-187s ◽  
Author(s):  
A M Mastro ◽  
A D Keith
Keyword(s):  
Rotational Motion ◽  
Spin Label ◽  
Mammalian Cells ◽  
Translational Motion ◽  
Diffusion Constant ◽  
Rotational Correlation Time ◽  
Model Systems ◽  
Quiescent Cells ◽  
Spin Resonance ◽  
In Cells

Measurements of diffusion of molecules in cells can provide information about cytoplasmic viscosity and structure. In a series of studies electron-spin resonance was used to measure the diffusion of a small spin label in the aqueous cytoplasm of mammalian cells. Translational and rotational motion were determined from the same spectra. Based on measurements made in model systems, it was hypothesized that calculations of the apparent viscosity of the cytoplasm from both rotational and translational motion would distinguish between the effects of viscosity and structure on diffusion. The diffusion constant measured in several cell lines averaged 3.3 X 10(-6) cm2/s. It was greater in growing cells and in cells treated with cytochalasin B than in quiescent cells. The viscosity of the cytoplasm calculated from the translational diffusion constant or the rotational correlation time was 2.0-3.0 centipoise, about two to three times that of the spin label in water. Therefore, over the dimensions measured by the technique, 50-100 A, solvent viscosity appears to be the major determinant of particle movement in cells under physiologic conditions. However, when cells were subjected to hypertonic conditions, the translational motion of the spin label decreased threefold, whereas the rotational motion changed by less than 20%. These data suggest that the decrease in cell volume under hypertonic conditions is accompanied by an increase in cytoplasmic barriers and a decrease in the space between existing cytoplasmic components without a significant increase in viscosity in the aqueous phase. In addition, a comparison of reported diffusion values of a variety of molecules in water and in cells indicates that cytoplasmic structure plays an important role in the diffusion of proteins such as bovine serum albumin.

scholarly journals A polymeric approach toward resistance-resistant antimicrobial agent with dual-selective mechanisms of action

2021 ◽  
Vol 7 (5) ◽  
pp. eabc9917
Author(s):  
Silei Bai ◽  
Jianxue Wang ◽  
Kailing Yang ◽  
Cailing Zhou ◽  
Yangfan Xu ◽  
...  
Keyword(s):  
Mammalian Cells ◽  
Mechanisms Of Action ◽  
Model Systems ◽  
General Strategy ◽  
Antimicrobial Polymers ◽  
Bacterial Dna ◽  
Bacterial Membranes ◽  
Severe Infections ◽  
Multiple Drugs ◽  
Resistance Rates

Antibiotic resistance is now a major threat to human health, and one approach to combating this threat is to develop resistance-resistant antibiotics. Synthetic antimicrobial polymers are generally resistance resistant, having good activity with low resistance rates but usually with low therapeutic indices. Here, we report our solution to this problem by introducing dual-selective mechanisms of action to a short amidine-rich polymer, which can simultaneously disrupt bacterial membranes and bind to bacterial DNA. The oligoamidine shows unobservable resistance generation but high therapeutic indices against many bacterial types, such as ESKAPE strains and clinical isolates resistant to multiple drugs, including colistin. The oligomer exhibited excellent effectiveness in various model systems, killing extracellular or intracellular bacteria in the presence of mammalian cells, removing all bacteria from Caenorhabditis elegans, and rescuing mice with severe infections. This “dual mechanisms of action” approach may be a general strategy for future development of antimicrobial polymers.

Thermotropic lipid and protein transitions in Chinese hamster lung cell membranes: relationship to hyperthermic cell killing

1983 ◽  
Vol 61 (6) ◽  
pp. 421-427 ◽  
Author(s):  
James R. Lepock ◽  
Kwan-Hon Cheng ◽  
Hisham Al-Qysi ◽  
Jack Kruuv
Keyword(s):  
Mammalian Cells ◽  
Plasma Membranes ◽  
Chinese Hamster ◽  
Cell Killing ◽  
Water Soluble ◽  
Growth Data ◽  
Protein Fluorescence ◽  
Polar Groups ◽  
Spin Resonance ◽  
Intrinsic Protein Fluorescence

Exposure of mammalian cells to hyperthermic temperatures (ca. 41–45 °C) appears to act as a direct or triggering effect to produce some later response such as cell death, thermotolerance, or heat-shock protein synthesis. The high activation energy of cell killing indicates that the direct effect of hyperthermia might be a thermotropic transition in some cellular component, for this particular response. Both hyperthermic survival and growth data imply that the temperature for the onset of hyperthermic cell killing is 40–41.5 °C for Chinese hamster lung V79 cells. Studies using the electron spin resonance label 2,2-dimethyl-5-dodecyl-5-methyloxazolidine-N-oxide and the fluorescent probe 1,6-diphenyl-1,3,5-hexatriene show the existence of lipid transitions at approximately 7–8 and 23–36 °C (or a broad transition between these temperatures) in mitochondria and whole cell homogenates, that correlate well with changes in growth and hypothermic killing. No lipid transition was detected near 40–41.5 °C that could correlate with hyperthermic killing in either mitochondrial or plasma membranes, but measurements of intrinsic protein fluorescence and protein fluorophore to trans-paranaric acid energy transfer demonstrate the existence of an irreversible transition in protein structure or arrangement above ca. 40 °C in both mitochondrial and plasma membranes. This transition is due to protein rearrangement and (or) unfolding such that there is increased exposure of protein tryptophan and tyrosine residues to polar groups and to paranaric acid. The strength of the transition implies that a significant fraction of total membrane protein is involved in this transition, which may be analogous to the heat-induced denaturation of water-soluble proteins. This alteration in membrane structure above ca. 40 °C could cause many of the observed changes in plasma membrane and mitochondrial function, which may further be involved in cellular responses to hyperthermia.

scholarly journals Dynamic Molecular Structure of DPPC-DLPC-Cholesterol Ternary Lipid System by Spin-Label Electron Spin Resonance

2004 ◽  
Vol 87 (4) ◽  
pp. 2483-2496 ◽  
Author(s):  
Yun-Wei Chiang ◽  
Yuhei Shimoyama ◽  
Gerald W. Feigenson ◽  
Jack H. Freed
Keyword(s):  
Molecular Structure ◽  
Electron Spin Resonance ◽  
Electron Spin ◽  
Spin Label ◽  
Spin Resonance ◽  
Lipid System

The interaction of ligands with chemically modified phosphorylase b

1976 ◽  
Vol 54 (5) ◽  
pp. 494-499
Author(s):  
D. Brooks ◽  
S. J. W. Busby ◽  
J. R. Griffiths ◽  
G. K. Radda ◽  
O. Avramovic-Zikic
Keyword(s):  
Conformational Changes ◽  
Spin Label ◽  
Native Enzyme ◽  
Carboxyl Groups ◽  
Chemically Modified ◽  
Allosteric Effector ◽  
Spin Resonance ◽  
Label Probe ◽  
Glycine Ethyl Ester ◽  
Modified Enzyme

Phosphorylase b which had been inactivated with 5-diazo-1H-tetrazole was specifically labelled with 4-iodoacetamidosalicylic acid (a fluorescent probe) or with N-(1-oxyl-2,2,6,6,-tetramethyl-4-piperidinyl)iodoacetamide (a spin label probe) so that the binding of ligands and accompanying conformational changes could be determined by fluorescence or electron spin resonance changes, respectively. The allosteric effector, AMP, causes conformational changes similar to those caused in the native enzyme. The affinity of binding of phosphate or AMP to the inhibited protein is the same as for the unmodified protein. The heterotropic interactions between glucose-1-phosphate or glycogen and AMP are much less in the inactivated enzyme than in unmodified phosphorylase. Using a light scattering assay, it is shown that the modified enzyme binds to glycogen less strongly than the native protein.Phosphorylase b which had been inactivated by carbodiimide in the presence of glycine ethyl ester, resulting in the modification of one or more carboxyl groups, was labelled with the spin label probe described above. The modified enzyme has an affinity for AMP similar to that of the native enzyme. AMP binding to the modified enzyme is tightened by glycogen, weakened by glucose-6-phosphate and is unaffected by glucose- 1-phosphate.The actions of 5-diazo-1H-tetrazole and carbodiimide on phosphorylase are discussed in the light of the above observations.

scholarly journals Antifungal Activities of Antineoplastic Agents:Saccharomyces cerevisiae as a Model System To Study Drug Action

1999 ◽  
Vol 12 (4) ◽  
pp. 583-611 ◽  
Author(s):  
Maria E. Cardenas ◽  
M. Cristina Cruz ◽  
Maurizio Del Poeta ◽  
Namjin Chung ◽  
John R. Perfect ◽  
...  
Keyword(s):  
Mammalian Cells ◽  
Kinase Inhibitor ◽  
Genetic Model ◽  
Fungal Infections ◽  
Study Drug ◽  
Drug Action ◽  
Mechanisms Of Action ◽  
Model Systems ◽  
Screening Tools ◽  
Sphingolipid Metabolism

SUMMARY Recent evolutionary studies reveal that microorganisms including yeasts and fungi are more closely related to mammals than was previously appreciated. Possibly as a consequence, many natural-product toxins that have antimicrobial activity are also toxic to mammalian cells. While this makes it difficult to discover antifungal agents without toxic side effects, it also has enabled detailed studies of drug action in simple genetic model systems. We review here studies on the antifungal actions of antineoplasmic agents. Topics covered include the mechanisms of action of inhibitors of topoisomerases I and II; the immunosuppressants rapamycin, cyclosporin A, and FK506; the phosphatidylinositol 3-kinase inhibitor wortmannin; the angiogenesis inhibitors fumagillin and ovalicin; the HSP90 inhibitor geldanamycin; and agents that inhibit sphingolipid metabolism. In general, these natural products inhibit target proteins conserved from microorganisms to humans. These studies highlight the potential of microorganisms as screening tools to elucidate the mechanisms of action of novel pharmacological agents with unique effects against specific mammalian cell types, including neoplastic cells. In addition, this analysis suggests that antineoplastic agents and derivatives might find novel indications in the treatment of fungal infections, for which few agents are presently available, toxicity remains a serious concern, and drug resistance is emerging.

scholarly journals Probing roto-translational diffusion of small anisotropic colloidal particles with a bright-field microscope

2021 ◽  
Vol 44 (4) ◽  
Author(s):  
Fabio Giavazzi ◽  
Antara Pal ◽  
Roberto Cerbino
Keyword(s):  
Particle Size ◽  
Rotational Motion ◽  
Colloidal Particles ◽  
Aqueous Suspension ◽  
Translational Motion ◽  
Translational Diffusion ◽  
Experimental Demonstration ◽  
Bright Field ◽  
Microscopic Scale ◽  
Bright Field Microscopy

Abstract Soft and biological materials are often composed of elementary constituents exhibiting an incessant roto-translational motion at the microscopic scale. Tracking this motion with a bright-field microscope becomes increasingly challenging when the particle size becomes smaller than the microscope resolution, a case which is frequently encountered. Here we demonstrate squared-gradient differential dynamic microscopy (SG-DDM) as a tool to successfully use bright-field microscopy to extract the roto-translational dynamics of small anisotropic colloidal particles, whose rotational motion cannot be tracked accurately in direct space. We provide analytical justification and experimental demonstration of the method by successful application to an aqueous suspension of peanut-shaped particles. Graphic abstract

scholarly journals Methylation of deoxyribonucleic acid in cultured mammalian cells by N-methyl-N′-nitro-N-nitrosoguanidine. The influence of cellular thiol concentrations on the extent of methylation and the 6-oxygen atom of guanine as a site of methylation

1970 ◽  
Vol 116 (4) ◽  
pp. 693-707 ◽  
Author(s):  
P. D. Lawley ◽  
Carolyn J. Thatcher
Keyword(s):  
Oxygen Atom ◽  
Nucleic Acids ◽  
Mammalian Cells ◽  
Dimethyl Sulphate ◽  
Biological Effects ◽  
Methylation Of Dna ◽  
Thiol Content ◽  
Cellular Thiol ◽  
In Cells

1. In neutral aqueous solution N-methyl-N′-nitro-N-nitrosoguanidine (MNNG) yields salts of nitrocyanamide as u.v.-absorbing products. With cysteine, as found independently by Schulz & McCalla (1969), the principal product is 2-nitràminothiazoline-4-carboxylic acid. Both these reactions liberate the methylating species; thiols enhance the rate markedly at neutral pH values. An alternative reaction with thiols gives cystine, presumably via the unstable S-nitrosocysteine. 2. Thiols (glutathione or N-acetylcysteine) in vitro at about the concentration found in mammalian cells enhance the rate of methylation of DNA markedly over that in neutral solution. 3. Treatment of cultured mammalian cells with MNNG results in rapid methylation of nucleic acids, the extent being greater the higher the thiol content of the cells. Rodent embryo cells are more extensively methylated than mouse L-cells of the same thiol content. Cellular thiol concentrations are decreased by MNNG. Proteins are less methylated by MNNG than are nucleic acids. 4. Methylation of cells by dimethyl sulphate does not depend on cellular thiol content and protein is not less methylated than nucleic acids. Methylation by MNNG may therefore be thiol-stimulated in cells. 5. Both in vitro and in cells about 7% of the methylation of DNA by MNNG occurs at the 6-oxygen atom of guanine. The major products 7-methylguanine and 3-methyladenine are given by both MNNG and dimethyl sulphate, but dimethyl sulphate does not yield O6-methylguanine. Possible reaction mechanisms to account for this difference between these methylating agents and its possible significance as a determinant of their biological effects are discussed.

Sign in / Sign up

Export Citation Format

Share Document