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Abstract

1The ATPase activity of the sarcoplasmic membranes and the phosphoryl transfer reaction from ATP to the membranes depend on the composition of their lipid phase.
2Lipid depletion leads to a drastic (∼ 60%) reduction of phosphoprotein formation. Oleate raises and lysolecithin decreases phosphoprotein formation. In absence of calcium and/or magnesium neither the native nor the delipidated vesicular preparations are phosphorylated.
3The ATPase activity of lipid-depleted vesicular preparations reactivated by oleate or lysolecithin and that of the preparation containing the lipid hydrolysis products after phospholipase A treatment reaches half-maximal activation at concentrations of ionized calcium between 0.2 and 0.3 μM. The maximal ATP-splitting rates, however, differ considerably.
4Half-maximum activation by Mg · ATP for the oleate and lysolecithin-reactivated ATPase is reached at 10 μM and 100 μM, respectively. The corresponding Hill coefficients are 0.5 and 0.6.
5For the oleate-reactivated ATPase an activation energy of about 35 kcal/mol has been calculated which is similar to that of the extra ATPase of native vesicles. The activation energy of the lysolecithin-reactivated ATPase is about 8 kcal lower.
6The ATPase activity of the reconstituted vesicular preparations shows an identical steep decline at pH values >7. An irreversible damage of the vesicular preparations at higher values could be excluded.
7The properties of the reconstituted sarcoplasmic ATPase are discussed in relation to the sarcoplasmic calcium transport.