A single copy of apolipoprotein B-48 is present on the human chylomicron remnant

Individuals homozygous for the e2 allele encoding apolipoprotein E exhibit a remnant removal defect and accumulate substantial levels of intestinally 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 antibody specific for selective binding and removal of apoB-100-containing lipoproteins. The unbound lipoproteins, termed chylomicron remnants, were particles with average hydrated diameters of 31.2 nm as determined by dynamic light scattering. They contained apoB-48 and ApoE as their only protein components. The number of apoB-48 molecules on each lipoprotein was assessed by counting the number of antibody molecules bound to the surface of the chylomicron remnants, using either a monoclonal 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 unable to transfer among lipoprotein particles, it may be inferred that nascent chylomicrons also contain a single copy of apoB-48.