Synthetic monoacylphospholipids as reactivators of the calcium-dependent ATPase of enzymatically delipidated sarcoplasmic membranes.

Abstract

1. The reactivating effect of synthetic analogues of natural lysophosphatidylcholines, acyldeoxyglycerophosphocholines, with acyl chain lengths between C10-C18 on enzymatically delipidated sarcoplasmic membranes has been analyzed. 2. The calcium-dependent ATPase is fully restored by myristoyldeoxyglycerophosphocholine. The restoring effect of deoxyglycerophosphocholines declines when the length of the saturated acyl chain becomes shorter or longer. 3. In contrast to the weakly effective palmitoyldeoxyglycerphosphocholine, its cis-9-mono unsaturated analogue oleyldeoxyglycerophosphocholine proved to be a highly effective reactivating compound. 4. The transfer of the terminal phosphate residue of ATP to the transport protein and the phosphate exchange between ADP and ATP displays the same dependence on the acyl chain length of the deoxyglycerophos-phocholines. In contrast to the ATPase activity the ATP-supported phosphoryltransfer reactions can only partially be restored. 5. A significant restoration of the phosphorylation of the protein by inorganic phosphate could be achieved with none of the deoxyglycerophosphocholines. 6. Below 23 degrees C the apparent activation energy of the calcium-dependent ATPase increases with increasing chain length of the deoxyglycerophosphoclines while above 23 degrees C the activation energies were identical for all restituted preparations.