title: Isolation of plasma and nuclear membranes of thymocytes. II. Biochemical composition.
abstract: Thymocyte plasma and nuclear membranes obtained by the procedure described in the accompanying paper were analyzed for their biochemical composition. Plasma membranes were very rich in phospholipid, cholesterol, sialic aicd; they did not contain nucleic acids. In comparison, nuclear membranes had a lower phospholipid to protein ratio and contained much less sialic acid and cholesterol. 50% of the cellular cholesterol and of the membrane-bound sialic acid were found in the plasma membranes, 14% in the nuclear membranes. Live cells were labeled with 131I, and the acid-insoluble radioactivity was followed in the subfractions. A good correlation with the distribution and enrichment of plasma membrane market-enzymes was obtained. Label enrichment was about 50-fold in the two lightest of the three plasma membrane fractions. 60% of the label was contained in the plasma membranes, only 4% in the nuclear membranes. Cross-contamination of these two types of membranes was thus negligible. Sodium dodecyl sulfate-gel electrophoresis revealed three different patterns specific for, respectively, plasma membranes, the microsomal-mitochondrial fraction, and nuclear membranes. Each pattern was characterized by a set of proteins and glycoproteins, among which high molecular weight glycoproteins could be considered as marker-proteins of, respectively, 280,000, 260,000, and 230,000 daltons. 131I-labeling of live cells tagged with a very high specific activity three glycoproteins of mol wt 280,000, 200,000, and 135,000 daltons. Nuclear membranes prepared from labeled isolated nuclei had a set of labeled proteins completely different from plasma membranes.
mesh_terms: D002458:Cell Fractionation; D002462:Cell Membrane / Q000032:analysis*; D002784:Cholesterol / Q000032:analysis; D006023:Glycoproteins / Q000032:analysis*; D008565:Membrane Proteins / Q000032:analysis*; D009685:Nuclear Envelope / Q000032:analysis*; D010743:Phospholipids; D012794:Sialic Acids / Q000032:analysis; D013601:T-Lymphocytes / Q000032:analysis / Q000648:ultrastructure*
chemical_list: D006023:Glycoproteins; D008565:Membrane Proteins; D010743:Phospholipids; D012794:Sialic Acids; D002784:Cholesterol