Sidedness of (Calcium, Magnesium) Adenosine Triphosphatase of Purified Torpedo Synaptic Vesicles

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Abstract
Purified Torpedo synaptic vesicles contain ouabain‐insensitive Mg2+τ and Ca2+‐stimulated ATPase activity. The sidedness of the ATPase on the vesicular membranes was investigated. Addition of ATP and Mg2+ or Ca2+ to intact vesicles results in activation of the ATPase. Exposure of the vesicles to low concentrations of Lubrol‐PX and Triton X‐100, which do not solubilize the activity, results in the concurrent release of the vesicular contents and in an increase of the Mg2+‐ATPase activity, whereas the Ca2+‐dependent activity is drastically decreased. p‐Chloromercuribenzene sulphonate (PCMBS) almost completely inhibits the activity of detergent‐treated vesicles whereas that of the native material is only slightly affected. Tryptic digestion of intact vesicles and of vesicular ghosts results in partial reduction of the ATPase activity. These results suggest that the vesicles contain an outward oriented Ca2+/Mg2+ ATPase activity which can be modulated by detergents.