scholarly journals Cl--stimulated adenosine triphosphatase: existence, location and function

1983 ◽  
Vol 106 (1) ◽  
pp. 143-161
Author(s):  
G. A. Gerencser ◽  
S. H. Lee
Keyword(s):  
Atpase Activity ◽  
Plasma Membranes ◽  
Direct Evidence ◽  
Chloride Transport ◽  
Indirect Evidence ◽  
Transport Processes ◽  
Animal Cells ◽  
Chemical Mechanisms ◽  
Mitochondrial Origin ◽  
And Function

The three universally accepted mechanisms of chloride transport across plasma membranes are: (i) sodium-coupled symport; (ii) anion-coupled antiport; and (iii) coupling to primary ion transport through electrical and/or chemical mechanisms. No direct evidence has been provided for primary chloride transport despite numerous reports of cellular, anion-stimulated ATPases and of chloride transport processes. Anion-stimulated ATPases are of mitochondrial origin and are a ubiquitous property of practically all animal cells. It also appears that there are other subcellular sites of anion-stimulated ATPase activity, especially the plasma membranes. Recent studies have provided indirect evidence (through parallel studies on the same tissue of anion-stimulated ATPase activity and chloride fluxes) which suggests a possible involvement of ATPase in net movement of chloride up its electrochemical gradient across plasma membranes. Further studies are required to substantiate a direct transport function to Cl--stimulated ATPases located in the plasma membrane.

Is there a Cl- pump?

1988 ◽  
Vol 255 (5) ◽  
pp. R677-R692
Author(s):  
G. A. Gerencser ◽  
J. F. White ◽  
D. Gradmann ◽  
S. L. Bonting
Keyword(s):  
Plasma Membrane ◽  
Atpase Activity ◽  
Membrane Fraction ◽  
Plasma Membranes ◽  
Direct Evidence ◽  
Objective Evaluation ◽  
Chemical Processes ◽  
Transport Processes ◽  
Cl Transport ◽  
Active Ion Transport

Three universally accepted mechanisms of Cl- transport across plasma membranes exist and they are 1) anion-coupled antiport, 2) cation-coupled symport, and 3) coupling to primary active ion transport through electrical and/or chemical processes. No unequivocal direct evidence has been provided for primary active Cl- transport (Cl- pump) despite numerous reports of cellular Cl- -stimulated adenosinetriphosphatase (ATPases) and of Cl- transport that cannot be accounted for by the three well-documented Cl- transport processes. It has been demonstrated that Cl- -stimulated ATPase activity is localized to both mitochondrial and microsomal aspects of the cellular apparatus. However, one group ascribes microsomal localization of Cl- -stimulated ATPase activity to mitochondrial contamination of that membrane fraction. Therefore, no Cl- pump could ever exist naturally in any plasma membrane. The other group simply states that there is plasma membrane localization of Cl- -stimulated ATPase activity that could function as a Cl- pump. Both arguments are logically advanced and their conclusions are consistent with their respective premises. Resolution to the question Is there a Cl- pump? rests with each reader's critique and objective evaluation.

Immunological approaches to gap junctions: Studies of immuno-localization, membrane protein topology, and function

1989 ◽  
Vol 47 ◽  
pp. 812-813
Author(s):  
Ross G. Johnson ◽  
Tze-Hong Lu ◽  
Kathleen Klukas ◽  
Larry Takemoto ◽  
S. Barbara Yancey
Keyword(s):  
Gap Junctions ◽  
Plasma Membranes ◽  
Strong Support ◽  
Membrane Domains ◽  
Biological Processes ◽  
Animal Cells ◽  
Membrane Protein Topology ◽  
A Cell ◽  
Clear Identification ◽  
And Function

It is now widely accepted that the plasma membranes of epithelial cells display a marked degree of polarity. This polarity is reflected in a number of parameters, e.g. the localization of certain proteins to basolateral membranes. Polarity is also illustrated by the presence of discrete membrane specializations, including desmosomes, tight junctions and gap junctions. These specializations provide strong support for the idea of membrane "domains" within the polarized membrane of the epithelial cell. This presentation relates to the proteins found in gap junction membranes. The issues include a clear identification of these proteins in different cells and an analysis of how a cell-to-cell channel is constructed by these proteins.The plasma membranes of most animal cells contain cell-to-cell channels, which provide for the direct, passive exchange of small molecules between cells. Collections of these channels are identified as "gap junctions." This form of intercellular communication is thought to be important in a wide variety of biological processes, including cellular differentiation, proliferation, and tissue homeostasis.

Structural similarity of ribosomes from E. coli and A. salina

1978 ◽  
Vol 36 (2) ◽  
pp. 242-243
Author(s):  
M. Boublik ◽  
R.M. Wydro ◽  
W. Hellmann ◽  
F. Jenkins
Keyword(s):  
Ribosomal Proteins ◽  
Direct Evidence ◽  
Structural Similarity ◽  
Carbon Support ◽  
Artemia Salina ◽  
Uranyl Acetate ◽  
Biological Assays ◽  
E Coli ◽  
And Function ◽  
Fine Carbon

Ribosomes are ribonucleoprotein particles necessary for processing the genetic information of mRNA into proteins. Analogy in composition and function of ribosomes from diverse species, established by biochemical and biological assays, implies their structural similarity. Direct evidence obtained by electron microscopy seems to be of increasing relevance in understanding the structure of ribosomes and the mechanism of their role in protein synthesis.The extent of the structural homology between prokaryotic and eukaryotic ribosomes has been studied on ribosomes of Escherichia coli (E.c.) and Artemia salina (A.s.). Despite the established differences in size and in the amount and proportion of ribosomal proteins and RNAs both types of ribosomes show an overall similarity. The monosomes (stained with 0.5% aqueous uranyl acetate and deposited on a fine carbon support) appear in the electron micrographs as round particles with a diameter of approximately 225Å for the 70S E.c. (Fig. 1) and 260Å for the 80S A.s. monosome (Fig. 2).

Localization of Adenosine Triphosphatase Activity in the Phleom of Nicotiana Tabacum

1972 ◽  
Vol 30 ◽  
pp. 230-231
Author(s):  
James Cronshaw ◽  
Jamison E. Gilder
Keyword(s):  
Plasma Membrane ◽  
Atpase Activity ◽  
Adenosine Triphosphatase ◽  
Higher Plants ◽  
High Surface ◽  
Root Tip ◽  
Animal Cells ◽  
Physiological Processes ◽  
Tip Cells ◽  
Atpase Localization

Adenosine triphosphatase (ATPase) activity has been shown to be associated with numerous physiological processes in both plants and animal cells. Biochemical studies have shown that in higher plants ATPase activity is high in cell wall preparations and is associated with the plasma membrane, nuclei, mitochondria, chloroplasts and lysosomes. However, there have been only a few ATPase localization studies of higher plants at the electron microscope level. Poux (1967) demonstrated ATPase activity associated with most cellular organelles in the protoderm cells of Cucumis roots. Hall (1971) has demonstrated ATPase activity in root tip cells of Zea mays. There was high surface activity largely associated with the plasma membrane and plasmodesmata. ATPase activity was also demonstrated in mitochondria, dictyosomes, endoplasmic reticulum and plastids.

scholarly journals Hepatic endosome fractions contain an ATP-driven proton pump

1985 ◽  
Vol 225 (1) ◽  
pp. 51-58 ◽  
Author(s):  
T Saermark ◽  
N Flint ◽  
W H Evans
Keyword(s):  
Endoplasmic Reticulum ◽  
Golgi Apparatus ◽  
Atpase Activity ◽  
Proton Pump ◽  
Subcellular Distribution ◽  
Plasma Membranes ◽  
Specific Activity ◽  
Ph Gradients ◽  
Subcellular Organelle ◽  
Liver Homogenates

Endosome fractions were isolated from rat liver homogenates on the basis of the subcellular distribution of circulating ligands, e.g. 125I-asialotransferrin internalized by hepatocytes by a receptor-mediated process. The distribution of endocytosed 125I-asialotransferrin 1-2 min and 15 min after uptake by liver and a monensin-activated Mg2+-dependent ATPase activity coincided on linear gradients of sucrose and Nycodenz. The monensin-activated Mg2+-ATPase was enriched relative to the liver homogenates up to 60-fold in specific activity in the endosome fractions. Contamination of the endosome fractions by lysosomes, endoplasmic reticulum, mitochondria, plasma membranes and Golgi-apparatus components was low. By use of 9-aminoacridine, a probe for pH gradients, the endosome vesicles were shown to acidify on addition of ATP. Acidification was reversed by addition of monensin. The results indicate that endosome fractions contain an ATP-driven proton pump. The ionophore-activated Mg2+-ATPase in combination with the presence of undegraded ligands in the endosome fractions emerge as linked markers for this new subcellular organelle.

scholarly journals Acetylcholine Receptors

1972 ◽  
Vol 60 (3) ◽  
pp. 248-262 ◽  
Author(s):  
H. Criss Hartzell ◽  
Douglas M. Fambrough
Keyword(s):  
Acetylcholine Receptors ◽  
Time Course ◽  
Plasma Membranes ◽  
Scintillation Counting ◽  
Receptor Density ◽  
Rat Diaphragm ◽  
Leg Muscles ◽  
And Function ◽  
Quantitative Radioautography ◽  
Ach Receptors

Using 125iodine-labeled α-bungarotoxin (α-BGT-125I) and quantitative radioautography, we have studied the time-course of the change in acetylcholine (ACh) receptor distribution and density occurring in rat diaphragm after denervation. In innervated fibers, ACh receptors are localized at the neuromuscular junction and the extrajunctional receptor density is less than five receptors per square micrometer. The extrajunctional receptor density begins to increase between 2 and 3 days after denervation and increases approximately linearly to 1695 receptors/µm2 at 14 days, subsequently decreasing to 529 receptors/µm2 at 45 days. We have isolated plasma membranes from rat leg muscles at various times after denervation and find that the change in concentration of ACh receptors in the membranes measured by α-BGT-125I binding and scintillation counting follows a time-course similar to the change in ACh receptor density measured radioautographically. Furthermore, we have correlated extrajunctional ACh receptor density measured by radioautography with extrajunctional ACh sensitivity measured by iontophoretic application of ACh and intracellular recording and find that the log of ACh receptor density is related to 0.53 times the log of ACh sensitivity. These results are discussed in terms of the electrophysiological experiments on the ACh receptor and the recent, more biochemical approaches to the study of ACh receptor control and function.

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