Isolation of chlordecone binding proteins from pig liver cytosol

Cytosolic proteins may play an important role in the transport of water insoluble substances through the cytosol to various subcellular locations. The binding of chlordecone (CD) to pig liver cytosolic proteins was studied after the simultaneous administration of [14C]CD and [3H]cholesterol via the portal vein. The isolation of chlordecone binding proteins (CDBPs), from liver cytosol consisted of repeated ultracentrifugation, ammonium sulfate fractionation, and chromatography on Bio-Gel A 0.5m, carboxymethyl cellulose (CMC), and Sephadex G-100. Three proteins retained [14C]CD after elution from the CMC column. CDBP I and CDBP II also retained [3H]cholesterol through this stage of purification, while CDBP III did not. The molecular weights, estimated by Sephadex G-100 gel filtration, were 33,500 and 67,000 for CDBP IA and CDBP IB, 49,000 for CDBP II, and 44,000 for CDBP III. Since dissociation of bound cholesterol could not be avoided during the purification procedures, binding of cholesterol to the CDBPs eluted from Sephadex G-100 was investigated. Incubation of CDBPs with [3H]cholesterol resulted in a 2000-fold increase of 3H associated with CDBP II, an 800-fold increase with CDBP IA, a 100-fold increase for CDBP IB, and a 300-fold increase for CDBP III. The isolation characteristics, molecular weights, and cholesterol binding properties of the CDBPs are compared with cytosolic cholesterol binding proteins previously isolated. The high specific activity binding of both CD and cholesterol by CDBP I and CDBP II suggests that CD and cholesterol share a common transport pathway in the liver cytosol.