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Query: UNIPROT:P06889 (Mol)
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Studies are presented that relate the calcium binding of isolated sarcolemmal membranes to myocardial contractility. The contractile strength of the perfused rabbit interventricular septum as a function of perfusate calcium concentration is compared with calcium bound to isolated rabbit sarcolemma at the same calcium concentrations. If the calcium-binding incubation medium contains 140 mM sodium chloride, the shapes of these two curves are identical. In another experiment, sarcolemmal calcium-binding data are compared with the results of Tillisch et al. (J. Mol. Cell. Cardiol. 11:137-148, 1979), who studied the response of rabbit papillary muscles to changes in the perfusate sodium concentration. Again a positive correlation between calcium bound and force developed is obtained. The results of experiments, using the isotope 22Na on the binding of sodium to isolated sarcolemmal membranes were subjected to Scatchard analysis. This revealed a single type of sodium receptor. The affinity constant for sodium binding is 110 M-1 and calcium appears to behave as a competitive inhibitor of sodium binding. The experimental results strongly imply a quantitative relationship between sarcolemmal calcium binding and myocardial contractility.
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PMID:Binding of Ca2+ and Na+ to sarcolemmal membranes: relation to control of myocardial contractility. 736 83

To determine the mechanism of apparent competitive binding of chloride and stilbenedisulfonates ( S ) to band 3 ( B ), we have compared the binding kinetics of three stilbenedisulfonates [ DIDS, 4,4'-diisothiocyanato-2, 2'-stilbenedisulfonate; H2DIDS 4,4'-diisothiocyanodihydro-2, 2'-stilbenedisulfonate and DBDS, 4,4'-dibenzamido-2, 2'-stilbenedisulfonate ] in the absence and presence of 150 mM sodium chloride at constant ionic strength. Biphasic time courses were observed with the fast phase rate constants following second-order kinetics, and the slow phase rate constants following saturation kinetics according to the mechanism: [formula: see text] The results can be understood in terms of the effect of chloride on each of these reaction steps. Chloride increased k1 by about 2-fold, but decreased k-1 8-fold for H2DIDS. Thus, 150 mM chloride increased the initial affinity of H2DIDS by about 19-fold. There was a 3-fold increase in the initial affinity for DIDS, but little or no effect of chloride on the initial affinity of DBDS. There was no effect of chloride on k2, but, previous "off" rate measurements showed that 150 mM chloride increases k-2 about 16-fold for DBDS and about 12-fold for H2DIDS. Taken together, these results indicate that chloride allosterically competes with stilbenedisulfonates for binding to band 3, predominantly by substantially shifting the second isomerization equilibrium to the left.
Biochem Mol Biol Int 1995 Aug
PMID:Effect of chloride on the binding kinetics of various stilbenedisulfonates to band 3. 758 Oct 2

Whereas horse apomyoglobin is fully unfolded at pH 2 in the absence of salt, addition of a salt such as sodium chloride or sodium trichloroacetate stabilizes the molten globule state. Thermal unfolding of the salt-stabilized molten globule states of horse apomyoglobin at pH 2 measured by far-UV circular dichroism occurs not only on heating (i.e. heat-denaturation) but also on cooling (i.e. cold-denaturation). This demonstrates that a hydrophobic interaction contributes to the stability of the molten globule state and suggests that the unfolding transition can be represented by a cooperative two-state mechanism. To clarify the mechanism of conformational transition, we investigated the thermal unfolding of the chloride-stabilized molten globule state by differential scanning calorimetry. We observed a broad but distinct excess heat capacity peak, which is consistent with the unfolding transition measured by circular dichroism. To further characterize the molten globule states, we examined by far-UV circular dichroism the denaturant-induced unfolding transitions of the molten globule states stabilized by sodium chloride or sodium trichloroacetate. The urea-induced unfolding transitions of the molten globule states were explained by the two-state mechanism. The guanidine-hydrochloride-induced unfolding experiments clarified that the trichloroacetate-stabilized molten globule state is distinct from the chloride-stabilized one and that the former involves additional helical segment(s). These results support a view that the thermal unfolding of the molten globule states at pH 2 can be approximated by a two-state transition. However, several results suggested that a combined mechanism incorporating the two-state transition and a gradual structural change would be more general in describing the conformational transition of the molten globule states.
J Mol Biol 1995 Jul 07
PMID:Thermodynamic stability of the molten globule states of apomyoglobin. 760 72

Standard visualization of nucleic acids by electron microscopy requires the use of special spreading techniques. The most common method takes advantage of the formation of a complex between negatively charged nucleic acid molecules and a positively charged monolayer film of proteins or cationic agents. Here, we describe an alternative protocol for the rapid visualization of DNA by electron microscopy based on the complexes formed when nucleic acids are exposed to buffers containing polyamines in the presence of sodium chloride. This procedure has been devised for the detection and analysis of large DNA molecules, such as yeast artificial chromosomes, but can be applied to DNA molecules of small size as well. The formation of DNA-polyamine complexes stabilizes large DNA molecules in solution and prevents shearing. This property allows large DNA molecules to remain intact after passage through microcapillaries used in the generation of transgenic mice by microinjection of fertilized eggs.
J Mol Biol 1995 Mar 03
PMID:Visualization of large DNA molecules by electron microscopy with polyamines: application to the analysis of yeast endogenous and artificial chromosomes. 787 69

Adventitious redox-active metals in Krebs-Henseleit buffer exhibit a significant enhancement of damage to isolated rat hearts. Using atomic absorption spectroscopy, it was determined that Krebs-Henseleit buffer contains substantial amounts of contaminating iron and copper. Significant copper contamination was found in ACS Reagent grade sodium chloride and sodium bicarbonate; iron contamination in sodium chloride, potassium chloride, sodium bicarbonate, and calcium chloride. Chelating resin treatment of individual reagents was found to decrease copper content of Krebs-Henseleit buffer from 0.32 to 0.17 microM. Using salicylate as a probe for .OH formation, it was determined that considerable amounts of this radical are formed when 0.25 mM ascorbate is added to the buffer indicating significant metal-catalysed autoxidation. Isolated rat hearts, perfused with non-chelexed Krebs-Henseleit buffer plus 0.25 mM ascorbate for 60 min, sustained moderate injury with developed systolic pressure, +dP/dtmax and -dP/dtmax decreased by 30 to 35% by the end of experiment. Hearts perfused with chelating resin-treated Krebs-Henseleit buffer sustained no significant injury within the same time frame. Furthermore, it was observed that hearts perfused with non-chelexed Krebs-Henseleit buffer accumulate significant amounts of copper depending on the amount of contamination and length of perfusion. Significant effects on post-ischemic end diastolic pressure were observed in hearts perfused with a Krebs-Henseleit buffer subsequently found to be contaminated with high levels of copper. These results clearly demonstrate that adventitious redox-active transition metals may be a confounding factor in experimental results. Further, it is recommended that all perfusion media be routinely examined for adventitious metals and treated if deemed necessary.
J Mol Cell Cardiol 1994 Jun
PMID:Adventitious redox-active metals in Krebs-Henseleit buffer can contribute to Langendorff heart experimental results. 852 67

The organization of sperm chromatin in the dasyurid marsupial, Sminthopsis crassicaudata, was investigated using various morphological techniques. Transmission electron microscopy indicates two quite distinct chromatin regions became evident late in spermiogenesis with an outer globular region containing blocks of very electron-dense chromatin. Fluorescent light microscopical studies after staining with DNA dyes and 7-amino actinomycin D of testicular, caput, and cauda epididymal spermatozoa showed that this region fluoresced less brightly than the rest of the nucleus, indicating the presence of fewer DNA binding sites. Freeze fracture showed that the chromatin in most of the nucleus had randomly arranged particles of various sizes, but that of the outer region was composed entirely of small particles. This outer region was more resistant to low concentrations of the ionic detergent, SDS, whereas both guanidine hydrochloride and urea together with sodium chloride generally dispersed all the chromatin except that in the outer globular region and in a localized area of the nucleus beneath the acrosome. This study has thus revealed that the outer globular chromatin of these spermatozoa responds differently to ionic detergents and protein denaturing agents and has a different chromatin organization than most of the rest of the nucleus. The significance of these differences remains, however, to be determined.
Mol Reprod Dev 1994 Jan
PMID:Unusual nuclear structure of the spermatozoon in a marsupial, Sminthopsis crassicaudata. 812 34

Crystals of the basic elicitin secreted by Phytophthora cryptogea have been obtained by the hanging-drop method of vapor diffusion from sodium chloride solutions. The crystals belong to the tetragonal space group P4(1)22 (or enantiomorph P4(3)22), with unit cell dimensions a = b = 47 A, c = 137 A and probably contain two molecules per asymmetric unit. The crystals are very stable to X-rays and diffract to 2.2 A resolution on a synchrotron radiation source.
J Mol Biol 1993 Jan 20
PMID:Crystallization and preliminary X-ray diffraction studies of beta-cryptogein, a toxic elicitin secreted by the phytopathogenic fungus Phytophthora cryptogea. 842 66

Collagens present in the connective tissues of the extracellular matrix of fibrosarcoma were isolated and characterized. The fibrosarcoma was induced in rats by the administration of 3-methylcholanthrene. The results obtained were compared with normal muscle. An excess amount of type V collagen was found to be produced by the fibrosarcoma tissue compared to the normal muscle. Type V collagen from fibrosarcoma was characterized on the basis of solubility behavior in sodium chloride solutions, electrophoretic mobility on SDS-polyacrylamide gels, elution pattern of phosphocellulose chromatography and amino acid composition.
Mol Cell Biochem 1993 Mar 10
PMID:Neoplastic association of enhanced type V collagen production in rat fibrosarcoma. 845 1

Simian immunodeficiency virus (SIV) proteinase has been crystallized from sodium acetate buffer with sodium chloride as precipitant. The crystals are orthorhombic and the space group is C222(1) with unit cell dimensions a = 32.18 A, b = 62.52 A, c = 95.76 A, alpha = beta = gamma = 90 degrees, indicating a single monomer of 10 kDa in the asymmetric unit. The crystals grow to dimensions of 0.2 mm x 0.2 mm x 0.07 mm within a week and are stable in the X-ray beam for at least 50 hours. A different crystal lattice was observed for SIV proteinase crystallized in the presence of pepstatin. The space group was P2(1)2(1)2(1) with cell dimensions of a = 35.26 A, b = 58.59 A, c = 93.95 A, alpha = beta = gamma = 90 degrees. Diffraction beyond 1.7 A was observed, indicating that a high resolution structure analysis is feasible.
J Mol Biol 1993 Jun 20
PMID:Crystallization and preliminary X-ray investigation of recombinant simian immunodeficiency virus proteinase. 851 73

Annexins, Ca2+- and phospholipid-binding proteins are known to bind to artificial and biological membranes in a calcium-dependent manner. However, the precise mechanism of the annexin-membrane interactions still remains to be studied in detail. In this paper we describe the results of studies on the interactions of the annexin/Ca complexes with phospholipids, obtained by the Wilhelmy balance method of assessing the surface pressure of a phospholipid monolayer. We show that the annexin IV/Ca as well as annexin VI/Ca complexes significantly reduce the surface pressure of a phosphatidylserine monolayer, when its initial value is close to collapse pressure. The effect is highly specific for monolayers composed of phosphatidylserine and strongly sensitive to pH and ionic strength. The most pronounced changes have been observed at pH 7.0-7.5, at a protein/Ca molar ratio of 1:2 for annexin IV and 1:4 for annexin VI. In the presence of sodium chloride at concentrations exceeding 400mM this effect was almost completely abolished. The obtained results point to the mainly electrostatic character of the annexin/phosphatidylserine interactions. In addition, using large multilamellar lipid vesicles and serine proteases, we demonstrate that annexins, when bound in a ternary complex with phospholipids and calcium ions, are partially protected against proteolysis. Our observation that annexin molecules, complexed with calcium ions, are protected against proteolytic attack in the presence of PS liposomes does not have to be necessarily explained in terms of partial penetration of protein within the membrane bilayer.
Mol Membr Biol
PMID:Interaction of annexins IV and VI with phosphatidylserine in the presence of Ca2+: monolayer and proteolytic study. 911 63


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