Localization of the amino phospholipids in sarcoplasmic reticulum membranes revealed by trinitrobenzenesulfonate and fluorodinitrobenzene.

The chemical probes for amino compounds 2,4,6-trinitrobenzensulfonate (TNBS) and 1-fluoro-2,4-dinitrobenzene (FDNB) were utilized to determine the localization of the amino phospholipids in the sarcoplasmic reticulum membranes. At low concentrations (less than 1 mM). TNBS does not penetrate the sarcoplasmic reticulum membrane, while FDNB readily penetrates it. The results show that about 70% of the total phosphatidylethanolamine is located on the external surface of the membrane, about 20% is on the internal surface and 10% is probably strongly interacting with the proteins since it is not accessible to the probes. In contrast, most of the phosphatidylserine is located on the inner surface of the membrane. This molecular distribution of the amino phospholipids supports a structural assymmetry of the sarcoplasmic reticulum membrane.