A SINGLE-COPY OF APOLIPOPROTEIN B-48 IS PRESENT ON THE HUMAN CHYLOMICRON REMNANT

Individuals homozygous for the e2 allele encoding apolipoprotein E exh ibit a remnant removal defect and accumulate substantial levels of int estinally derived particles containing apolipoprotein B-48 (apoB-48). Such lipoproteins were isolated from the plasma of E2/E2 individuals, and further purified by affinity chromatography using a polyclonal ant ibody specific for selective binding and removal of apoB-100-containin g lipoproteins. The unbound lipoproteins: termed chylomicron remnants, were particles with average hydrated diameters of 31.2 nm as determin ed by dynamic light scattering. They contained apoB-48 and ApoE as the ir only protein components, The number of apoB-48 molecules on each li poprotein was assessed by counting the number of antibody molecules bo und to the surface of the chylomicron remnants, using either a monoclo nal antibody specific for a single epitope on apoB-48 or a mixture of two such monoclonal antibodies specific for widely separated epitopes. The results of this analysis seem unambiguous: no more than one apoB- 48 resides on the chylomicron remnant. Because apoB appears to be unab le to transfer among lipoprotein particles, it may be inferred that na scent chylomicrons also contain a single copy of apoB-48.