Binding of the Ca2+,Mg2+-activated adenosine triphosphatase of Escherichia coli to phospholipid vesicles

Incubation of the Ca2+,Mg2+-activated adenosine triphosphatase of Escherichia coli with phospholipid vesicles resulted in binding of the enzyme to the lipid. Binding was observed with vesicles of soybean phospholipid (asolectin), phosphatidyglycerol, phosphatidylserine, phosphatidylcholine, and cardiolpin. Binding was not affected by alterations in pH in the range of pH 6.5 to 8.5, by ionic strength, or by the presence of Mg2+. Loss of the delta subunit from the enzyme had no effect on binding. However, removal of the delta and epsilon subunits by treatment of the enzyme with trypsin prevented binding to phospholipid. This treatment also removed a small portion (less than 2000 daltons) of the alpha subunit. It is concluded that the ATPase of E. coli binds to phospholipid vesicles mainly by nonpolar interactions through the alpha and (or) epilson subunits of the enzyme.