scholarly journals Sucrose Release into the Endosperm Cavity of Wheat Grains Apparently Occurs by Facilitated Diffusion across the Nucellar Cell Membranes

1995 ◽  
Vol 109 (2) ◽  
pp. 579-585 ◽  
Author(s):  
N. Wang ◽  
D. B. Fisher
Keyword(s):  
Cell Membranes ◽  
Facilitated Diffusion ◽  
Nucellar Cell ◽  
Wheat Grains

scholarly journals Estimates of Michaelis-Menten Constants for the Two Membranes of the Brain Endothelium

1984 ◽  
Vol 4 (2) ◽  
pp. 241-249 ◽  
Author(s):  
Albert Gjedde ◽  
Ove Christensen
Keyword(s):  
Steady State ◽  
Endothelial Cell ◽  
Transport Properties ◽  
Glucose Transport ◽  
Cell Membranes ◽  
Experimental Studies ◽  
Facilitated Diffusion ◽  
Capillary Endothelial Cells ◽  
The Individual ◽  
Tracer Experiments

Tracer studies on facilitated diffusion across the blood–brain barrier lead to the calculation of Michaelis-Menten constants that describe the rate of transport. However, the barrier consists of two endothelial cell membranes, and the relevance of single Michaelis-Menten constants in relation to the two cell membranes is unknown. We have formulated a model of two endothelial cell membranes and show that the measured Michaelis-Menten constants are simple functions of the properties of the individual membranes when transport across the endothelium is rapid ( P1 > 10−6 cm s−1). We also show that the Michaelis-Menten constants determined in tracer experiments describe facilitated diffusion in the steady state only if the two membranes have similar transport properties. As an application of this observation, we have examined three experimental studies that measure glucose transport in the steady state and show that the Michaelis-Menten constants for glucose transport calculated from the tracer experiments are equal to the constants calculated from the steady-state experiments. We conclude that the luminal and abluminal membranes of brain capillary endothelial cells have equal glucose transport properties.

Modeling and Characterization of a Chemomechanical Actuator Based on Protein Transporters

2007 ◽  
Author(s):  
Vishnu Baba Sundaresan ◽  
Donald J. Leo
Keyword(s):  
Cell Membrane ◽  
Cell Membranes ◽  
Fluid Transport ◽  
Sucrose Concentration ◽  
Yeast Cells ◽  
Facilitated Diffusion ◽  
Flux Rate ◽  
Artificial Membrane ◽  
Saturation Concentration ◽  
Protein Transporters

Plants and animal cells are naturally occurring actuators that exhibit force and motion driven by fluid transport through the cell membrane. The protein transporters embedded in the cell membrane serve as the selective gateway for ion and fluid transport. The actuator presented in this work generates force and deformation from mass transport through an artificial membrane with protein transporters extracted from plant cell membranes. The artificial membrane is formed from purified 1-Palmitoyl-2-Oleoyl-sn-Glycero-3-[Phospho-L-Serine] (Sodium Salt) (POPS), 1-Palmitoyl-2-Oleoyl-sn-Glycero-3-Phosphoethanolamine (POPE) lipids and supported on a porous substrate. The protein transporter used in the actuator membrane is a proton-sucrose cotransporter, SUT4, extracted from yeast cells that genetically modified to grow the cotransporter in their cell membranes. The SUT4 transporter conducts proton and sucrose from the side of the membrane with higher concentration and carries water molecules across the membrane. It is observed from transport characterization experiments that fluid flux through the membrane varies with the applied sucrose concentration and hence is chosen as the control stimulus in the actuator. A modified four-state facilitated diffusion model is applied to the transport characterization data to compute the two characteristic parameters for fluid transport, saturation concentration and translocation rate, through the membrane. The flux rate through the membrane is observed to increase with the concentration till a particular value and saturates at a higher concentration. The concentration at which the flux rate through the membrane saturates is referred to as the saturation concentration. The saturation concentration for the actuator is experimentally found to be 6±0.6mM sucrose on the side with lower pH. The corresponding maximum translocation rate is found to be 9.6±1.2 nl/μ.cm2.min. The maximum steady state deformation produced by the actuator is observed at 30 mM sucrose that corresponds to a force of 0.89 mN.

Uric acid distribution volume calculated by kinetic modeling and extracellular volume predicted by bioimpedance method

2020 ◽  
Vol 43 (11) ◽  
pp. 701-709
Author(s):  
Toru Shinzato ◽  
Shigeru Nakai ◽  
Takahito Ito ◽  
Kazuhiko Shibata ◽  
Teppei Matsuoka ◽  
...  
Keyword(s):  
Uric Acid ◽  
Mass Balance ◽  
Blood Test ◽  
Cell Membranes ◽  
Extracellular Volume ◽  
Distribution Volume ◽  
Facilitated Diffusion ◽  
Bioimpedance Analysis ◽  
Test Results ◽  
Simple Diffusion

Background: Several reports indicate that extracellular volume predicted by bioimpedance analysis method is associated with hydration status of hemodialysis patients. Theory: Fundamentally, uric acid does not cross cell membranes by simple diffusion, either by facilitated diffusion or by active transport. In addition, uric acid cannot move through cell membranes in most tissues other than those involved in uric acid excretion. These facts support the interpretation that uric acid distribution volume would therefore correlate with extracellular volume. Methods: We examined correlation between uric acid distribution volume calculated by uric acid mass-balance modeling from regular blood test results and extracellular volume predicted by bioimpedance analysis predicted by BCM (Fresenius Medical Care) in 53 patients. Results: There was a significant correlation between uric acid distribution volume ( x) and extracellular volume predicted by bioimpedance analysis ( y): y = 0.69 x + 3.39, r2 = 0.61, p < 0.0001. Bland–Altman analysis showed systematic error for uric acid distribution volume versus extracellular volume predicted by bioimpedance analysis (mean difference between uric acid distribution volume and extracellular volume predicted by bioimpedance analysis was 0.94 L, 95% confidence interval of difference was −3.29 to 5.17 L). Conclusion: Uric acid distribution volume calculated by uric acid mass-balance modeling from regular blood test results may be an alternative marker of extracellular volume predicted by bioimpedance analysis.

Photoreceptor disk membrane substructures by means of the complementary freeze-fracture-replica methods

1978 ◽  
Vol 36 (2) ◽  
pp. 156-157
Author(s):  
A. Tonosaki ◽  
M. Yamasaki ◽  
H. Washioka ◽  
J. Mizoguchi
Keyword(s):  
Cell Membranes ◽  
Freeze Fracture ◽  
Purple Membrane ◽  
Remarkable Case ◽  
Single Face ◽  
Disk Membrane ◽  
Associated Proteins ◽  
Photoreceptor Membranes

A vertebrate disk membrane is composed of 40 % lipids and 60 % proteins. Its fracture faces have been classed into the plasmic (PF) and exoplasmic faces (EF), complementary with each other, like those of most other types of cell membranes. The hypothesis assuming the PF particles as representing membrane-associated proteins has been challenged by serious questions if they in fact emerge from the crystalline formation or decoration effects during freezing and shadowing processes. This problem seems to be yet unanswered, despite the remarkable case of the purple membrane of Halobacterium, partly because most observations have been made on the replicas from a single face of specimen, and partly because, in the case of photoreceptor membranes, the conformation of a rhodopsin and its relatives remains yet uncertain. The former defect seems to be partially fulfilled with complementary replica methods.

Introduction to Cell Membranes at Molecular Resolution

1978 ◽  
Vol 36 (3) ◽  
pp. 497-502
Author(s):  
R.J. Barrnett
Keyword(s):  
Cell Membranes ◽  
International Federation ◽  
Mountain Range ◽  
Cellular Membranes ◽  
Short History ◽  
Biological Organization ◽  
Macromolecular Assemblies ◽  
The Past

This subject, is like observing the panorama of a mountain range, magnificent towering peaks, but it doesn't take much duration of observation to recognize that they are still in the process of formation. The mountains consist of approaches, materials and methods and the rocky substance of information has accumulated to such a degree that I find myself concentrating on the foothills in the foreground in order to keep up with the advance; the edifices behind form a wonderous, substantive background. It's a short history for such an accumulation and much of it has been moved by the members of the societies that make up this International Federation. My panel of speakers are here to provide what we hope is an interesting scientific fare, based on the fact that there is a continuum of biological organization from biochemical molecules through macromolecular assemblies and cellular membranes to the cell itself. Indeed, this fact explains the whole range of towering peaks that have emerged progressively during the past 25 years.

664: CXCL12/CXCR4 Trans-Activation of HER2 in Lipid Rafts of Prostate Cancer Cell Membranes Promotes Bone Metastasis

2007 ◽  
Vol 177 (4S) ◽  
pp. 223-223
Author(s):  
Sreenivasa R. Chinni ◽  
Hamilto Yamamoto ◽  
Zhong Dong ◽  
Aaron Sabbota ◽  
Sanaa Nabha ◽  
...  
Keyword(s):  
Prostate Cancer ◽  
Bone Metastasis ◽  
Lipid Rafts ◽  
Cancer Cell ◽  
Cell Membranes ◽  
Prostate Cancer Cell

Transport of zinc and manganese to developing wheat grains

1995 ◽  
Vol 95 (3) ◽  
pp. 449-455 ◽  
Author(s):  
J. N. Pearson ◽  
Z. Rengel ◽  
C. F Jenner ◽  
R. D. Graham
Keyword(s):  
Wheat Grains

The Uptake of Adenine by Isolated Human Platelet Membranes

1974 ◽  
Vol 32 (02/03) ◽  
pp. 457-464
Author(s):  
Paul C. French ◽  
Jan J. Sixma ◽  
Holm Holmsen
Keyword(s):  
Human Platelet ◽  
Facilitated Diffusion ◽  
Adenine Phosphoribosyltransferase ◽  
Ph Optimum ◽  
Intact Cells ◽  
Platelet Membranes ◽  
Group Translocation ◽  
Triton X

SummaryAdenine uptake into isolated platelet membranes had about the same Km (151 ± 21 • 9 nM) as uptake into intact cells (159 ± 21 nM) and was also competitively inhibited by papaverine and hypoxanthine. No uptake occurred at 0° and accumulated adenine was converted to AMP. AMP was not firmly bound to protein as judged by chromatography of triton X-100 solubilized membranes on Sephadex G25. The pH optimum for adenine uptake was at pH 5-5. Exogenous 5-phosphoribosyl-l-pyrophos- phate strongly stimulated uptake. These data may be explained by uptake of adenine by facilitated diffusion followed by conversion to AMP by adenine phosphoribosyltransferase but group translocation cannot be entirely excluded.

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