JBC, Vol. 251, Issue 17, 5161-5165, Sep, 1976
Phospholipid-protein interactions in the Ca2+-adenosine triphosphatase of sarcoplasmic reticulum
A. F. Knowles, E. Eytan and E. Racker
Ca2+-adenosine triphosphatase from sarcoplasmic reticulum has been
delipidated by gel filtration through a Sephadex G-200 column equilibrated
with buffer containing cholate. The delipidated Ca2+-adenosine
triphosphatase had negligible adenosine triphosphatase activity, but up to
50% of the ATPase activity was restored when the delipidated enzyme was
recombined with phosphilipids. It was shown with the delipidated
preparation that the phosphorylation of the enzyme by either ATP or Pi was
entirely dependent on phospholipids. Among the purified phospholipids,
phosphatidylcholine reactivated the adenosine triphosphatase activity
better than phosphatidylethanolamine. Vesicles capable of translocating
Ca2+ were reconstituted from delipidated Ca2+-adenosine triphosphatase and
phosphatidylethanolamine, but not with phosphatidylcholine alone. We
conclude that the firmly bound phospholipids which are purified together
with the adenosine triphosphatase protein are not essential for the pump
since they can be substituted by phosphatidylethanolamine isolated from
soybeans.