Functional Approach to the Catalytic Site of the Sarcoplasmic Reticulum Ca2+-ATPase: Binding and Hydrolysis of ATP in the Absence of Ca2

Isolated sarcoplasmic reticulum vesicles in the presence of Mg^sup 2+^ and absence of Ca^sup 2+^ retain significant ATP hydrolytic activity that can be attributed to the Ca^sup 2+^-ATPase protein. At neutral pH and the presence of 5 mM Mg^sup 2+^, the dependence of the hydrolysis rate on a linear AT...

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Veröffentlicht in:Journal of bioenergetics and biomembranes 2004-06, Vol.36 (3), p.265
Hauptverfasser: Lax, Antonio, Soler, Fernando, Fernández-belda, Francisco
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Sprache:eng
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Zusammenfassung:Isolated sarcoplasmic reticulum vesicles in the presence of Mg^sup 2+^ and absence of Ca^sup 2+^ retain significant ATP hydrolytic activity that can be attributed to the Ca^sup 2+^-ATPase protein. At neutral pH and the presence of 5 mM Mg^sup 2+^, the dependence of the hydrolysis rate on a linear ATP concentration scale can be fitted by a single hyperbolic function. MgATP hydrolysis is inhibited by either free Mg^sup 2+^ or free ATP. The rate of ATP hydrolysis is not perturbed by vanadate, whereas the rate of p-nitrophenyl phosphate hydrolysis is not altered by a nonhydrolyzable ATP analog. ATP binding affinity at neutral pH and in a Ca^sup 2+^-free medium is increased by Mg^sup 2+^ but decreased by vanadate when Mg^sup 2+^ is present. It is suggested that MgATP hydrolysis in the absence of Ca^sup 2+^ requires some optimal adjustment of the enzyme cytoplasmic domains. The Ca^sup 2+^-independent activity is operative at basal levels of cytoplasmic Ca^sup 2+^ or when the Ca^sup 2+^ binding transition is impeded.[PUBLICATION ABSTRACT]
ISSN:0145-479X
1573-6881
DOI:10.1023/B:JOBB.0000031978.15139.49