Solenoid Siberian snakes have successfully maintained polarization in particle rings below 1 GeV, but never in multi-GeV rings, because the spin rotation by a solenoid is inversely proportional to ...the beam momentum. High energy rings, such as Brookhaven’s 255 GeV Relativistic Heavy Ion Collider (RHIC), use only odd multiples of pairs of transverse B-field Siberian snakes directly opposite each other. When it became impractical to use a pair of Siberian Snakes in Fermilab’s 120GeV/c Main Injector, we searched for a new type of single Siberian snake that could overcome all depolarizing resonances in the 8.9–120GeV/c range. We found that a snake made of one 4-twist helix and 2 dipoles could maintain the polarization. This snake design could solve the long-standing problem of significant polarization loss during acceleration of polarized protons from a few GeV to tens of GeV, such as in the AGS, before injecting them into multi-hundred GeV rings, such as RHIC.
We have previously shown that plasma membrane calcium ATPase (PMCA) pump activity is affected by the membrane protein concentration (Vanagas et al., Biochim Biophys Acta 1768:1641–1644,
2007
). The ...results of this study provided evidence for the involvement of the actin cytoskeleton. In this study, we explored the relationship between the polymerization state of actin and its effects on purified PMCA activity. Our results show that PMCA associates with the actin cytoskeleton and this interaction causes a modulation of the catalytic activity involving the phosphorylated intermediate of the pump. The state of actin polymerization determines whether it acts as an activator or an inhibitor of the pump: G-actin and/or short oligomers activate the pump, while F-actin inhibits it. The effects of actin on PMCA are the consequence of direct interaction as demonstrated by immunoblotting and cosedimentation experiments. Taken together, these findings suggest that interactions with actin play a dynamic role in the regulation of PMCA-mediated Ca
2+
extrusion through the membrane. Our results provide further evidence of the activation–inhibition phenomenon as a property of many cytoskeleton-associated membrane proteins where the cytoskeleton is no longer restricted to a mechanical function but is dynamically involved in modulating the activity of integral proteins with which it interacts.
Calcium Occlusion in Plasma Membrane Ca2+-ATPase Ferreira-Gomes, Mariela S.; González-Lebrero, Rodolfo M.; de la Fuente, María C. ...
Journal of biological chemistry/The Journal of biological chemistry,
09/2011, Letnik:
286, Številka:
37
Journal Article
Recenzirano
Odprti dostop
In this work, we set out to identify and characterize the calcium occluded intermediate(s) of the plasma membrane Ca2+-ATPase (PMCA) to study the mechanism of calcium transport. To this end, we ...developed a procedure for measuring the occlusion of Ca2+ in microsomes containing PMCA. This involves a system for overexpression of the PMCA and the use of a rapid mixing device combined with a filtration chamber, allowing the isolation of the enzyme and quantification of retained calcium. Measurements of retained calcium as a function of the Ca2+ concentration in steady state showed a hyperbolic dependence with an apparent dissociation constant of 12 ± 2.2 μm, which agrees with the value found through measurements of PMCA activity in the absence of calmodulin. When enzyme phosphorylation and the retained calcium were studied as a function of time in the presence of LaIII (inducing accumulation of phosphoenzyme in the E1P state), we obtained apparent rate constants not significantly different from each other. Quantification of EP and retained calcium in steady state yield a stoichiometry of one mole of occluded calcium per mole of phosphoenzyme. These results demonstrate for the first time that one calcium ion becomes occluded in the E1P-phosphorylated intermediate of the PMCA.
The autoinhibition/activation of the PMCA (plasma membrane Ca2+-ATPase) involves conformational changes in the membrane region of the protein that affect the amount of lipids directly associated with ...the transmembrane domain. The lipid-protein-dependence of PMCA isoforms 2 and 4 expressed and obtained in purified form from Saccharomyces cerevisiae was investigated using the phosphatidylcholine analogue 125ITID-PC/16 {l-O-hexadecanoyl-2-O-9-2-125Iiodo-4-(trifluoromemyl-3H-diazirin-3-yl)benzyloxycarbonylnonanoyl-sn-glycero-3-phosphocholine}, which was incorporated into mixtures of dimyristoylphosphatidylcholine and the non-ionic detergent C12E10 deca(ethylene glycol) dodecyl ether. We found no differences between the recombinant PMCA4 and PMCA purified from erythrocytes (ePMCA). However, titration of the half-maximal activation by Ca2+/calmodulin of PMCA2 showed 30-fold higher affinity than PMCA4. PMCA2 exhibited a lower level of labelling in the autoinhibited conformation relative to PMCA4, indicating that the lower autoinhibition was correlated with a lower exposure to lipids in the autoinhibited state. Analysis of the lipid-protein stoichiometry showed that the lipid annulus of PMCA varies: (i) in accordance to the conformational state of the enzyme; and (ii) depending on the different isoforms of PMCA. PMCA2 during Ca2+ transport changes its conformation to a lesser extent than PMCA4, an isoform more sensitive to modulation by calmodulin and acidic phospholipids. This is the first demonstration of a dynamic behaviour of annular lipids and PMCA.
The aim of this study was to investigate the rumen bacteria in terms of genetic biodiversity and variation due to different physical form of corn in cow diet. A total of twenty dry cows were fed for ...3 months with the same diet, only differed for corn physical form, ten received corn grains, while the other ones received corn flour. To investigate the biodiversity of the bacterial 16S rRNA gene clone library analysis has been conducted and then the sequencing has been carried out using Ion Torrent PGM™ System. Bacterial population was tested using R statistical software. The Kruskal-Wallis one-way analysis of variance (Kruskal-Wallis, 1952) confirmed that the bacterial populations were different when the animals were fed grain compared with flour corn. Both the OUT’s abundance (Operational Taxonomic Unit) and the biodiversity indexes presented a significant difference among the two sample groups, underlining the large changes that take place even with small diet modifications in ruminal environment. There is still the need to deepen how exactly the diet changes the rumen phylogenetic structure and the consequences on bacteria’s activity.
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