Dual character of lipid composition of the envelope membrane of spinach chloroplasts

The envelope membrane was isolated from intact spinach chloroplastsby gentle osmotic treatment in a medium containing appropriateamounts of cations to prevent dissociation and fragmentationof the thylakoids. This treatment allowed us to separate effectivelythe envelope membranes from the thylakoids with one-step (0.6M/0.9 M) sucrose density gradient centrifugation. The envelope membrane contained both glyceroglycolipids andglycerophospholipids, as does the thylakoid membrane. Therewere, however, notable differences in the relative amounts oflipid components between these two membranes. The major glyceroglycolipidin the envelope membrane was digalactosyl diglyceride, whereasmonogalactosyl diglyceride was the major one in the thylakoid.The envelope membrane was characterized by a high content ofglycerophospholipids, as much as three-fold that in the thylakoidmembrane. Phosphatidyl choline, which is known to be minor inthe thylakoids and abundant in the microsomal and mitochondrialmembranes, was a major component, accounting for 50% of thetotal glycerophospholipids. The dual character of lipid compositionof the envelope membrane is discussed in terms of its chemicaland structural connection to the other intracellular membranesystems. (Received May 26, 1975; )