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  • enzyme kinetics  (2)
  • liposome stability  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Molecular and cellular biochemistry 120 (1993), S. 119-126 
    ISSN: 1573-4919
    Keywords: liposome stability ; liposome-blood interaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Lipid composition and specially their electrostatic properties, were found to greatly influence the stability of liposomes in human blood serum. The amount and type of serum proteins bound to the liposomes were also clearly influenced by lipid composition and charge of liposomes. a good correlation was found between the amount of serum proteins adsorbed to a given type of liposome and its instability as measured by the release of an encapsulated fluorescent probe. Liposomes that bind the highest amount of protein were the least stable, except for the case of liposomes containing gangliosides, which were fairly stable even at a high amount of bound protein. Liposomes with neutral charge containing phosphatidylcholine were the most stable and bound the lowest amount of protein. Liposomes with positive charge behaved similarly to those with neutral charge. However, the stability of negatively charged liposomes was very dependent on their composition. Those liposomes containing only one class of negatively charged phospholipids bound a great amount of protein and were very unstable. However, those liposomes containing also phosphatidylcholine bound less protein and were more stable. The examination of the electrophoresis patterns of serum proteins bound to the different types of liposomes indicated the presence of specific proteins which correlated with liposome instability. (Mol Cell Biochem120: 119–126, 1993)
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    ISSN: 1573-6881
    Keywords: (Ca2+ + Mg2+)-ATPase ; sarcoplasmic reticulum ; membrane fluidity ; enzyme kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract (Ca2+ + Mg2+)-ATPase from sarcoplasmic reticulum has been reconstituted with dipalmitoylphosphatidylcholine, and the activating effect of ATP and Ca2+ on this enzyme has been studied at different temperatures. It has been found that two kinetic forms of the enzyme are interconverted at about 31°C, and this is possibly related to a phase change in the phospholipid which is more directly associated with the protein. Above 31°C the enzyme is less dependent on ATP activation at high ATP concentrations but shows positive cooperativity for Ca2+ activation. On the other hand, below 31°C, the reconstituted enzyme is more dependent on ATP for activation at high ATP concentrations than the purified ATPase and does not show cooperativity for Ca2+ activation.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    ISSN: 1573-6881
    Keywords: (Ca2+-Mg2+)-ATPase ; sarcoplasmic reticulum ; enzyme kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract The (Ca2+-Mg2+)-ATPase from sarcoplasmic reticulum presents negative cooperativity for the hydrolysis of Mg2+-ATP at different concentration ranges of this substrate. A kinetic model is proposed according to which Mg2+-ATP may bind to three different enzymatic species present during the catalytic cycle, E (K 1=1 µM), E′∼P.Ca2 (K 9=500 µM) and *EP (K 7=20 µM), accelerating the release of Pi. The fact that each of these species has a different affinity for Mg2+-ATP allows a significant enhancement of the rate of Pi release to the medium at the different ranges of Mg2+-ATP concentration where the enzyme shows a kinetic cooperativity. The kinetic analysis of this mechanism yields an equation which is a ratio of two cubic polynomials (3:3 rate equations) with respect to Mg2+-ATP and which may explain the negative cooperativity of the enzyme at different concentration ranges of Mg2+-ATP.
    Type of Medium: Electronic Resource
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