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  • 1
    Electronic Resource
    Electronic Resource
    Inhibition of (Na/K)-ATPase by electrophilic substances: Functional implications (1995)
    Springer
    Molecular and cellular biochemistry 147 (1995), S. 187-192 
    Details
    ISSN: 1573-4919
    Keywords: (Na/K)-ATPase ; electrophilic reagents ; cation binding site ; isolated perfused heart ; 5-nitrofurylethylene
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract The effect of electrophilic substances: p-bromophenylisothiocyanate (PBITC); fluoresceinisothiocyanate (FITC); [4-isothiocyanatophenyl-(6-thioureidohexyl)-carbamoylmethyl]-ATP (ATPITC); 2,4,6-trinitrobezenesulfonic acid (TNBS); 1-(5-nitro-2-furyl)-2-phenylsulfonyl-2-furylcarbonyl ethylene (FE1); 1-(5-phenylsulfonyl-2-furyl)-2-phenylsulfonyl-2-furylcarbonyl ethylene (FE2) and 1-(5-phenylsulfonyl-2-furyl)-2-phenylsulfonyl-2-tienocarbonyl ethylene (FE3) on the sarcolemmal (Na/K)-ATPase isolated from guinea-pig hearts was studied. FITC and PBITC were found to inhibit competitively the activation of (Na/K)-ATPase by ATP. Being for the enzyme inhibitor and substrate at the same time ATPITC does not offered clear kinetic behavior. However, the activation of (Na/K)-ATPase by sodium and potassium ions was inhibited non-competitively by all three isothiocyanates. These data indicated that isothiocyanates may interact predominantly in the ATP-binding site of the enzyme molecule. In contrary to isothiocyanates TNBS and FE1 (FE2 and FE3 were ineffective) inhibited the activation of (Na/K)-ATPase by ATP non-competitively i.e., their interaction in the ATP-binding site seemed to be improbable. Nevertheless, TNBS and FE1 both manifested affinities to that moiety of (Na/K)-ATPase molecule which is binding potassium. More specific was the effect of FE1 that showed clearly competitive inhibition of potassium-stimulation of the enzyme activity. FE1 exerted also an ouabain-like effect on the mechanical activity of isolated perfused guinea-pig heart. This result indicates that FE1 seems to exert a selective inhibition of the (Na/K)-ATPase not only in vitro but also in integrated cardiac tissue.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00944800
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  • 2
    Electronic Resource
    Electronic Resource
    Influence of global ischemia on the sarcolemmal ATPases in the rat heart (1995)
    Springer
    Molecular and cellular biochemistry 147 (1995), S. 99-103 
    Details
    ISSN: 1573-4919
    Keywords: cardiac sarcolemma ; (Na,K)-ATPase ; Mg-ATPase ; Ca-ATPase ; enzyme kinetics ; activation energy ; ischemia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract To elucidate the effect of global ischemia on the energy utilizing processes, regarding the molecular principles, the kinetic and thermodynamic properties of the sarcolemmal ATPases were investigated in the rat heart. The activation energy for hydrolysis of ATP during ischemia was higher when the reaction was catalyzed by Ca-ATPase or Mg-ATPase. For the Na,K-ATPase reaction, no changes in the activation energy were observed. With respect to the enzyme kinetics, ischemia in a timedependent manner induced important alterations in KM and Vmax values of Na,K-ATPase, Ca-ATPase and Mg-ATPase. The Vmax value decreased significantly already after 15 min of ischemia, and it also remained low after 30, 45 and 60 min for all 3 enzymes. The significant diminution of KM values occurred later in the 30th min for Ca-ATPase, in the 45th min for Na,K-ATPase. The observed drop in KM indicates the increase in the affinity of the enzymes to substrate, suggesting thus the adaptation to ischemic conditions on the molecular level. This effect could be attributed to some conformational changes of the protein molecule in the vicinity of the ATP-binding site developing after longer duration of ischemia.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00944789
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    Paper (German National Licenses)
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