Partial purification and characterization of the low density lipoprotein receptor from bovine adrenal cortex

The low density lipoprotein (LDL) receptor has been solubilized from bovine adrenocortical membranes with octyl-beta-D-glucoside and purified 350-fold in the presence of the detergent. The activity of the solubilized receptor was assayed by precipitating the receptor with acetone in the presence of egg phosphatidylcholine liposomes. the receptor-phosphatidylcholine liposomes bound 125I-LDL with the same affinity and specificity as did the native LDL receptor of intact membranes. The complex of receptor and octylglucoside had a Stokes radius of 53.5 A as determined by agarose gel filtration. The sedimentation coefficient, s20,w, of the receptor . octylglucoside complex was 7.3 as determined by metrizamide density gradient centrifugation. An identical value for the sedimentation coefficient was obtained when deuterium oxide was substituted for water in the metrizamide gradient. These data were used to derive an estimate of 163,000 for the molecular weight of the LDL receptor . octylglucoside complex (range of molecular weight, 152,000 to 170,000). The receptor is an acidic protein as determined by its behavior on ion exchange chromatography. In the most highly purified LDL receptor preparation, which had been subjected to the sequential steps of solubilization, DEAE-cellulose chromatography, agarose gel filtration, and phosphatidylcholine/acetone precipitation, the receptor was estimated to constitute about 5% of the total protein. Thus, complete purification of the LDL receptor from bovine adrenocortical membranes will require an additional 20-fold purification, or a total purification of about 7,000-fold.