ATPase functions

TBT < TET < TMT inhibit the cardiovascular system in a concentration-dependent manner which affects the Ca+2 pump as well as protein phosphorylation. The compounds also inhibited the Ca+2-Atpase function similar to that observed with nerve cells35. 

Jorgensen, P.L., Hakansson, K.O., Karlish, S.J.D. (2003) Structure and mechanism of Na,K-ATPase functional sites and their interactions. Annu. Rev. Physiol. 65, 817-849. 

Rosado, J.A., Saavedra, F.R., Redondo, P.C., Hernandez-Cruz, J.M., Salido, G.M., Pariente, J.A., 2004, Reduced plasma membrane Ca2+-ATPase function in platelets from patients with non-insulin-dependent diabetes mellitus. Haematologica 89, 1142-1144. 

In the cell, the vacuolar ATPase functions exclusively as an ATP hydrolysis-driven proton pump. This functional preference of the vacuolar ATPase seems not to be due to a fundamental structural difference compared with the ATP synthase because it has been shown that the V-ATPase can be reversed to synthesize ATP in vitro, albeit with very low efficiency (Hirata et al., 2000). 

Although hydrogenase linked H2 production does not require ATP utilization, normal aerobic fixation of atmospheric CO2 does. As will be discussed below, when CO2 fixation does not occur (as is the case under anaerobic, sulfur-deprived condi tions), the accumulation of ATP molecules in the stroma inhibits ATPase function. This results in the non dissipation of the proton gradient and causes the build-up of the proton motive force. It has been shown that, under these conditions, photosynthetic electron transport is down regulated917 and consequently reductant is not available for efficiently producing H2.140... 

Copper ion homeostasis in prokaryotes involves Cu ion efflux and sequestration. The proteins involved in these processes are regulated in their biosynthesis by the cellular Cu ion status. The best studied bacterial Cu metalloregulation system is found in the gram-positive bacterium Enterococcus hirae. Cellular Cu levels in this bacterium control the expression of two P-type ATPases critical for Cu homeostasis (Odermatt and Solioz, 1995). The CopA ATPase functions in Cu ion uptake, whereas the CopB ATPase is a Cu(I) efflux pump (Solioz and Odermatt, 1995). The biosynthesis of both ATPases is regulated by a Cu-responsive transcription factor, CopY (Harrison et al., 2000). In low ambient Cu levels Cop Y represses transcription of the two ATPase genes. On exposure to Cu(I), CopY dissociates from promoter/operator sites on DNA with a for Cu of 20 jlM (Strausak and Solioz, 1997). Transcription of copA and copB proceeds after dissociation of CuCopY. The only other metal ions that induce CopY dissociation from DNA in vitro are Ag(I) and Cd(II), although the in vivo activation of copA and copB is specihc to Cu salts. The CuCopY complex is dimeric with two Cu(I) ions binding per monomer (C. T. Dameron, personal communication). The structural basis for the Cu-induced dissociation of CopY is unknown. Curiously, CopY is also activated in Cu-dehcient cells, but the mechanism is distinct from the described Cu-induced dissociation from DNA (Wunderh-Ye and Solioz, 1999). 

The impact of the H1069Q mutation on Wilson ATPase function has previously been tested by functional complementation, but the findings... 

In spite of the experimental evidence, the role of the Na-K-ATPase in the formation of the palytoxin channel has not been clarified in detail. The recent advances in the understanding of the Na-K-ATPase function have recently allowed Artigas and Gadsby (2003) to postulate that palytoxin could disrapt the strict coupling between the pump s inner and outer gates, allowing them to both be open. Thus, it is not clear whether the paly toxin-sensitive chaimel is located within the enzyme and the step(s) in the normal functioning of the pump(s) that are affected by palytoxin remain to be elucidated. 

Two main possibilities are apparent. Subunit III might be an essential functional part of the proton pump, in which case its most essential structures may be expected to be built into the two subunits of Paracoccus. Unfortunately, the primary structures of the latter are not yet known. The absence of DCCD-sensitivity does not discount this possibility. Bacterial mutants are known, for example, in which the H -ATPase functions properly but has lost the sensitivity towards DCCD, although the potential DCCD-binding residue is retained in the primary structure [175]. The... 

Chlordane blocks the neuronal uptake of chloride ions by blocking the activity of y-amino butyric acid. This results in only a partial depolarization of activated neurons leading to an uncontrolled excited condition. Additionally, chlordane inhibits Ca, Mg -adenosine triphosphate (ATPase) and Na, K -ATPase functions, leading to increased concentrations of intracellular free calcium in neurons and the release of neurotransmitters. This neurotransmitter release potentiates depolarization of adjacent neurons in a chain reaction manner, propagating stimuli through the central nervous system (CNS). 

Hunter GW, Negash S, Squier TC. Phosphatidylethanolamine modulates Ca-ATPase function and dynamics. Biochemistry 1999 38 1356-1364. 

Hunter, G. W Negash, S and Squier, T. C, (1999). Phos-phaiidylethanolaminc modulates Ca " -ATPase function and dynamics, fliof /uujii.sfry 38(4), 1356-1364,... 

Rao US. Mutation of glycine 185 to valine alters the ATPase function of the human P-glycoprotein expressed in Sf9 cells. J Biol Chem 1995 270 6686-6690. 

The concept of an apolar (hydrophobic)-polar (e.g., charge) repulsive free energy of hydration, AG,p, contributes to understanding the mechanism whereby ATPases function in three distinguishing respects. First and second, ATP binding, and particularly on hydrolysis with formation of ADP plus Pi, has the potential to effect both push and pull components of force. Third, release of Pi results in development of an elastic pull component of force that is most in evidence during isometric contractions. These three elements of force development are discussed immediately below. 

As discussed below in section 8.4.4.11, ATP binding provides the major push component of force, but we expect the peak in AG.p to occur at the moment of hydrolysis when the charge concentration is greatest with the momentary presence of both ADP and Pj In the synthesis function of the Fi motor of ATP synthase, we expect that the maximum repulsion occurs between the most hydrophobic side of the rotor and the ADP and Pj state and that this maximal repulsion decreases on ATP formation, which, in the consiUent view, drives ATP formation. Accordingly, because repulsion is the force that drives the ATPase function of the Fi motor and because repulsion drives rotation, ATP binding would provide near-maximal force generation, enhanced only at the moment of hydrolysis to form ADP plus Pj. 

The most profound and fundamental prediction of the hydrophobic consilient mechanism, as regards Fi-ATPase function, is that hydrolysis to form ADP and Pi provides a water-mediated burst of apolar-polar repulsion that would drive the y-rotor in the ATPase mode... 

Proton-ATPases can be divided into three classes a) The plasma-membrane type, which operates via a phosphoenzyme intermediate and therefore is part of the P-ATPase superfamily. These proton pumps evolved from a common ancestor of the Ca" and Na pumps and are structurally distinct from the other two families of proton pumps (1-3). b) The eubacterial-type F-ATPases that are present in eubacteria, mitochondria and chloroplasts (3,4). c) The vacuolar-type V-ATPases that are present in archaebacteria and the vacuolar system of eukaryotic cells (2-6). F and V-ATPases are structurally and functionally related and have evolved from a common ancestral enzyme (3,4). This relationship was established from a wealth of sequence information regarding F-ATPases and by more recent studies on V-ATPases. The divergent pathways by which F and V-ATPases have evolved were recently elucidated by pai lel studies in several laboratories (3). It is the piupose of this communication to discuss aspects pertinent to the evolution of CFq-CFi, which is the F-ATPase functioning in photosynthesis. 

An nNOS type NOS is present in cardiac sarcoplasmic reticulum membrane (Xu et al. 1999) and both nNOS and eNOS are associated with cardiac sarcolenunal membrane (Zhou et al. 2000). Cardiac sarcolenunal (Na K )-ATPase is an important integral membrane protein that catalyses Na and active transport across the plasma membrane (Skou 1998). Lack of NOS isoforms in cardiac muscle significantly altered both (Na lC)-ATPase activity and sarcoplasmic reticulum Ca -ATPase function (Zhou et al. 2002). 

The plasma membrane contains an enzyme that catalyzes the export of Ca + from the cytoplasm at the expense of ATP hydrolysis. The Ca +-ATPase has features that place it in the category of plasma membrane enzymes that also includes the Na+/K+-ATPase and the H+-ATPase. The Ca +-ATPase functions to keep the cytosolic Ca +concentration low (< 1 fiM). It is not a major contributor to the generation of the membrane potential or to the energetics of the transport of bioorganic molecules. 

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