31P NMR as a tool for monitoring detergent solubilization of sarcoplasmic reticulum membranes

Abstract

Sarcoplasmic reticulum vesicles were solubilized stepwise by the nonionic detergent octaethyleneglycol monododecyl ether; 31P NMR enabled the extent of phospholipid solubilization to be monitored by following the conversion of the broad resonance peak characterizing the phospholipids inserted in the bilayer to the narrow resonance signal characterizing phospolipids inserted into a mixed micelle. Up to 0.25 g detergent/g protein could be incorporated into the membrane without solubilization. Higher detergent concentrations of up to 1.5–2 g detergent/g protein led to gradual solubilization. Although the method allows us to monitor the extent of solubilization of individual phospholipid classes, there was no evidence of either preferential solubilization or retention of a specific class of phospholipids.