Reactivation of lipid-depleted Ca2+-ATPase by a nonionic detergent.

The Ca2+-ATPase of sarcoplasmic reticulum can be reversibly delipidated by precipitation with polyethyleneglycol in the presence of deoxycholate and glycerol to as low as 4 mol of phospholipid/mol of enzyme polypeptide and can then be reactivated to 90% of its original ATPase activity by the addition of phosphatidylcholine. Furthermore, the preparation exhibits nearly the same activity if the nonionic detergent dodecyl octaoxyethyleneglycol monoether is substituted for the added phospholipid. The delipidated ATPase is soluble in the detergent and retains activity for several days. This is the first report of the Ca2+-ATPase retaining high activity with less than about 30 mol of phospholipid bound per mol of polypeptide.