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Purified adenosine triphosphatase (F1-ATPase) (EC 3.6.1.3) from Micrococcus lysodeikticus membranes required divalent metal ions for its reattachment to membranes depleted of the enzyme. This requirement showed specificity: Mg2+ ions were able to reconstitute a physiologically significant F1-ATPase-membrane complex, whereas Zn2+ ions produced one differing from the native and the Mg2+-reconstituted ATPase-membrane complexes. Micrococcus lysodeikticus membranes contained a limited number of specific binding sites, which did not seem to be modified after ATPase release and membrane manipulation. The binding properties of F1-ATPase preparations correlated well with their content of δ-subunit. The results suggested that F1-ATPase molecules able to rebind to M. lysodeikticus membranes must contain at least two copies of the δ-subunit. The isolated subunits (particularly α- and β-subunits) showed a certain capacity for rebinding to the membranes, but an enzyme form consisting only of α- and β-subunits was unable to reattach to membranes. These results prove unambiguously that δ-, but not α-or any other polypeptide, was involved in the attachment of F1-ATPase to M. lysodeikticus membranes, unlike other bacterial F1-ATPases. These results were consistent with a subunit stoichiometry and arrangement: α3 β3 γ(1-2) δ2-Mg2+- membrane.
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