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arXiv · 2401.17382

Functional approach to the catalytic site of the sarcoplasmic reticulum Ca(2+)-ATPase: binding and hydrolysis of ATP in the absence of Ca(2+)

A Lax·F Soler·F Fernandez Belda
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Abstract

Isolated sarcoplasmic reticulum vesicles in the presence of Mg(2+) and absence of Ca(2+) retain significant ATP hydrolytic activity that can be attributed to the Ca(2+)-ATPase protein. At neutral pH and the presence of 5 mM Mg(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(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(2+)-free medium is increased by Mg(2+) but decreased by vanadate when Mg(2+) is present. It is suggested that MgATP hydrolysis in the absence of Ca(2+) requires some optimal adjustment of the enzyme cytoplasmic domains. The Ca(2+)-independent activity is operative at basal levels of cytoplasmic Ca(2+) or when the Ca(2+) binding transition is impeded.

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A Lax, F Soler, F Fernandez Belda. 2024-01-30. Functional approach to the catalytic site of the sarcoplasmic reticulum Ca(2+)-ATPase: binding and hydrolysis of ATP in the absence of Ca(2+). https://doi.org/10.1023/b%3Ajobb.0000031978.15139.49.

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