Membrane ion pumps

It is now generally accepted that auxin and low-pH-induced stimulation of elongation growth results from a temporary weakening or relaxation of the wall.400,469,470,473-477 There is some evidence that such hormones as auxin activate, within the cell membrane, ion pumps that lower the pH of the wall,400,468,477,478-481 and it was suggested that the direct... 

A recently identified thyroid hormone cell surface receptor on the extracellular domain of integrin alphaVbeta (3) leads to the activation of the mitogen-activated protein kinase (MAPK) signal transduction cascade in human cell lines, Examples of MAPK-dependent thyroid hormone actions are plasma membrane ion pump stimulation and specific nuclear events, These events include serine phosphorylation of the nuclear thyroid hormone receptor, leading to co-activator protein recruitment and complex tissue responses, such as thyroid hormone-induced angiogenesis, The existence of this cell surface receptor means that the activity of the administered hormone could be limited through structural modification of the molecule to reproduce only those hormone actions initiated at the cell surface (8,9). 

Extrapolating from well-characterized enzymatic inhibition in test tubes, numerous mechanistic ideas concerning the in vivo effects of vanadium compounds have been advanced. The effects of vanadium compounds as transition-state analogs of certain enzymes with a phosphoprotein intermediate in their reaction scheme is proposed to account for the action of vanadium [11] in many biological systems. Unfortunately, it is often difficult to determine if the inhibition observed in the test tube occurs in vivo. For example, although vanadate is a potent inhibitor of plasma membrane ion pumps (such as the sodium potassium ATPase) in the test tube, it is difficult to determine if these pumps are actually inhibited in animals exposed to vanadium compounds. Currently, the role of vanadium compounds as protein phosphatase (PTP) inhibitors is believed to be related to the metabolic effects of this... 

The active sites of these enzymes can have a nitrogen ligand, usually as histidine (acid phosphatases and some protein phosphatases), a nucleophilic serine residue (alkaline phosphatases), a cysteine residue in which the thiol group can form a covalent species with the phosphate ester (protein phosphatases), or an aspartate-linked phosphate (plasma membrane ion pumps). The inhibitory form of vanadium is usually anionic vanadate V(V), but cationic vanadyl V(IV) has also shown strong inhibition of some types of phosphorylase reactions. Above neutral pH, speciation of vanadyl ions produces anionic V(IV) species capable of inhibition of enzymes in the traditional transition-state analogue manner [5],... 

Vanadium was first used in France in 1899 as a therapeutic agent for diabetes [119] however, this experimental result was buried with time. The modem era of studying the antidiabetic properties of vanadium began in 1979, when it was shown that vanadium was present in muscle and inhibited plasma membrane ion pumps [1], Experiments were then done in tissue culture experiments, where vanadium... 

Some ions (Na, K, Ca ", CF) act as specific charge carriers, with concentration gradients maintained and modified by membrane ion pumps and trigger mechanisms. Sudden changes in these concentration gradients are signals for nerve or muscle action. 

In the erythrocyte, glycolysis, the pentose phosphate pathway, and the metabolism of 2,3-bisphosphoglycerate (Chapter 28) are the predominant pathways of carbohydrate metabolism. Glycolysis supplies ATP for membrane ion pumps and NADH for reoxidation of methemoglobin. The pentose phosphate pathway supplies NADPH to... 

Prior to cellular excitation, an electrical gradient exists between the inside and the outside of the cell membrane. At this time, the cell is polarized. In atrial and ventricular conducting tissue, the intracellular space is about 80 to 90 mV negative with respect to the extracellular environment. The electrical gradient just prior to excitation is referred to as resting membrane potential (RMP) and is the result of differences in ion concentrations between the inside and the outside of the cell. At RMP, the cell is polarized primarily by the action of active membrane ion pumps, the most notable of these being the sodium-potassium pump. For example, this specific pump (in addition to other systems) attempts to maintain the intracellular sodium concentration at 5-15 mEq/L and the extracellular sodium concentration at 135-142 mEq/L and the intracellular potassium concentration at 135-140 mEq/L and the extracellular potassium concentration at 3-5 mEq/L. RMP can be calculated by using the Nemst equation ... 

Bacteriorhodopsin is unique among membrane proteins because of its central role in many different scientific disciplines and its use as the proving ground for many different scientific approaches such as laser spectroscopy, membrane biophysics, and molecular biology (1-6). In addition, bacteriorhodopsin has attained a new prominence, not only because it is used as a model of membrane ion pumps, but also because it is increasingly important for such technological applications as advanced photonic and photoelectronic... 

We now know a great deal about the structure of cell membranes, ion pumps, electroporation, and membrane channels. In membrane reconstitution experiments, the evidence is that intracellular signal transduction begins at membrane receptors. The work... 

Membrane ion pumps consist of assemblies of large macromolecules that span the thickness of the phospholipid cell membrane, as illustrated in Fig. 17.2. The pumps for sodium and potassium ion are coupled and appear to be a single structure that acts somewhat like a turnstile. Their physical construction transports sodium and potassium in opposite directions in a 3 2 atomic ratio, respectively. 

Membranes also have a finite and distributed electric resistance both across their thickness and along their length. These resistances tend to short circuit the membrane capacitor and cause its stored charge to decay to zero if the membrane ion pumps cease. There are several different models of the cell membrane that describe its static and transient bioelectric behavior. Models of the cell membrane are useful because they help explain the propagation of action events, such as that along a nerve. 

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