ATPase transport proteins

The Clinical-Molecular Interface Congestive Heart Failure and the NaVK" ATPase Transporter Protein... 

In addition to direct inhibition of the vesicular transport protein, storage of neurotransmitters can be reduced by dissipation of the proton electrochemical gradient. Bafilomycin (a specific inhibitor of the vacuolar H+-ATPase), as well as the proton ionophores carbonyl cyanide m-chlorophenylhydrazone (CCCP) and carbonylcyanide p-(trifluoromethoxy) phenylhy-drazone (FCCP) are used experimentally to reduce the vesicular storage of neurotransmitters. Weak bases including amphetamines and ammonium chloride are used to selectively reduce ApH. 

Investigations of the cellular effects of radiofrequency radiation provide evidence of damage to various types of avian and mammalian cells. These effects involve radiofrequency interactions with cell membranes, especially the plasma membrane. Effects include alterations in membrane cation transport, Na+/K+-ATPase activity, protein kinase activity, neutrophil precursor membrane receptors, firing rates and resting potentials of neurons, brain cell metabolism, DNA and RNA synthesis in glioma cells, and mitogenic effects on human lymphocytes (Cleary 1990). 

Some of these environmental aspects are obvious, such as anthropogenic sources of chemicals that disrupt the structure of delicate epithelia involved in solute transport, or directly inhibit the solute transporting proteins (e.g. Cu inhibition of Na+K+ ATPase [82]). The general effects of environmental stress are also well known, since many of the hormones released into the blood during stressful situations will alter the activity of ion transporters (e.g. corticosteroids, catecholamine [14]). 

Figure 1.3 Selective-binding sites in transport proteins for Na+, K+, Ca2+ and Cl. (a) Two Na+ binding sites in the LeuT Na+-dependent pump, (b) Four K+ binding sites in the KcsA K+ channel, (c) Two Ca2+ binding sites in the Ca2+ ATPase pump, (d) Two central Cl binding sites in a mutant C1C Cl /H+ exchanger. (From Gouax and MacKinnon, 2005. Copyright (2005) American Association for the Advancement of Science.)...

Ankyrins are intracellular proteins that associate with a variety of transport proteins including Na+ channels, Na +, K+ ATPase, Na +, Ca2+ exchange, Ca2+ release channels. 

There are, however, various types of active transport systems, involving protein carriers and known as uniports, symports, and antiports as indicated in Figure 3.7. Thus, symports and antiports involve the transport of two different molecules in either the same or a different direction. Uniports are carrier proteins, which actively or passively (see section "Facilitated Diffusion") transport one molecule through the membrane. Active transport requires a source of energy, usually ATP, which is hydrolyzed by the carrier protein, or the cotransport of ions such as Na+ or H+ down their electrochemical gradients. The transport proteins usually seem to traverse the lipid bilayer and appear to function like membrane-bound enzymes. Thus, the protein carrier has a specific binding site for the solute or solutes to be transferred. For example, with the Na+/K+ ATPase antiport, the solute (Na+) binds to the carrier on one side of... 

The depletion of GSH and NADPH will allow the oxidation of protein sulfydryl groups, which may be an important step in the toxicity. Thus, GSH and protein sulfydryl groups, such as those on Ca2+-transporting proteins, are important for the maintenance of intracellular calcium homeostasis. Thus, paracetamol and NAPQI cause an increase in cytosolic calcium, and paracetamol inhibits the Na+/K+ ATPase pump in isolated hepatocytes. 

While reconstitution of the calcium-dependent ATPase from the lipid deprived enzyme can easily be achieved, attempts to reconstitute simultaneously the abolished accumulation of calcium had no success55,70. Yet, in a number of reports the reconstitution of calcium transport from the enzyme after purification and/or after lipid exchange has been described160,, 70 172) jn these experiments it was attempted to reconstitute vesicles which could retain calcium ions which were transported into the vesicular space by the transport protein across the lipid bilayer. Different lipid pro-... 

Calcium ions are bound with an identical high affinity of 5.106M by the purified ATPase, by the transport protein in the native membranes as well as by partially deli-pidated, reversibly inactivated membrane preparations"8, ll9 173). The amount of calcium which is bound with that high affinity corresponds to two sites per transport molecule. The observed affinity is in good agreement with the affinity derived from the dependence on ionized calcium of the activation of calcium uptake and ATP splitting as well as of the inhibition of calcium release and ATP synthesis18 u2,, 74 17s Since the latter experiments were performed under conditions which provide a constant internal free calcium concentration by the presence of oxalate or phosphate in the system, the reactions must have been activated or inhibited by the calcium ions... 

Measurements of the steady state phosphoprotein level at different temperatures revealed that phosphoprotein formation is accompanied by a large and constant enthalpy change of 48 kJ/mol. In contrast, the likewise quite high activation energy of phosphoprotein formation exhibits a pronounced break between 20°C and 30°C. A break in the Arrhenius plot of the calcium-dependent ATPase has been observed in the same temperature range and has been interpreted as transitions between two activity states of the enzyme. Apparently, the phosphorylation of the calcium free protein by inorganic phosphate exhibits a similar kind of activity transition as observed for the calcium-dependent interaction of the transport protein with ATP131. A similar transition phenomenon complicates the time course of phosphoprotein formation... 

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