Ca(2+)-dependency and substrate specificity of cholinergic synaptic vesicle ATPase.
H Stelzl1, E J Grondal, H Zimmermann
1AK Neurochemie, Zoologisches Institut der J. W. Goethe-Universität, Siesmayerstr 70, D-6000 Frankfurt am Main, Federal Republic of Germany.
Neurochemistry International
|May 27, 2010
Summary
Cholinergic synaptic vesicles possess a single Mg(2+)-ATPase, not a Ca(2+)-stimulated one. This enzyme preferentially hydrolyzes ATP, and Ca(2+) uptake is not mediated by this Mg(2+)-ATPase.
Area of Science:
- Neuroscience
- Biochemistry
- Cell Biology
Background:
- Cholinergic synaptic vesicles are crucial for neurotransmission.
- Understanding the ion transport mechanisms within these vesicles is vital.
Purpose of the Study:
- To investigate the nature of the Mg(2+)-ATPase in cholinergic synaptic vesicles.
- To determine if a Ca(2+)-stimulated Mg(2+)-ATPase exists in these vesicles.
- To clarify the mechanism of ATP-stimulated Ca(2+) uptake.
Main Methods:
- Purification of cholinergic synaptic vesicles from Torpedo electric organ.
- Enzyme kinetic analysis of ATPase activity.
- Controlled measurements of Ca(2+) dependency.
Main Results:
- The Mg(2+)-ATPase activity showed limited activation (46%) by millimolar Ca(2+).
- ATP was preferentially hydrolyzed over other tri-nucleotides upon Mg(2+)-activation, but not Ca(2+)-activation.
- No Mg(2+)-dependent, Ca(2+)-stimulated ATPase was detected across a range of free Ca(2+) concentrations.
Conclusions:
- Cholinergic synaptic vesicles contain a single type of ATPase, primarily stimulated by Mg(2+).
- The observed ATP-stimulated Ca(2+) uptake by vesicles is not mediated by a Mg(2+)-ATPase responsive to micromolar Ca(2+).
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