Apolipoprotein[a] is not associated with apolipoprotein B in human liver.
The aim of this research was to determine whether apolipoprotein[a] (apo[a]) is linked to apolipoprotein B (apoB) in human liver. Four ELISAs were developed: 1) a competition assay that measures apoB; 2) a competition assay that measures apo[a]; 3) a capture assay based on capture of apo[a] by a polyclonal antibody and detection of co-immobilized apoB using a monoclonal antibody; and 4) a capture assay based on capture of apo[a] using a polyclonal antibody and detection of immobilized apo[a] using a monoclonal antibody. Assays 2 and 4, therefore, measure apo[a] either free or in complex with other proteins, while assay 3 measures apo[a] associated with apoB. The levels of apo[a] ranged from 25 to 440 micrograms/g liver in nine individual liver samples. There was no significant difference between apo[a] levels in individual human liver samples measured using ELISA 1 or 3; however, it was not possible to detect apo[a]/apoB using assay 3. ApoB was present in human liver homogenates at levels ranging from 90 to 700 micrograms/g measured using assay 1. These results suggest, therefore, that apo[a] is not coupled to apoB in the liver and may be secreted in the free form to bind with low density lipoprotein (LDL) in the extracellular fluid or plasma.
Department of Molecular Biology and Biotechnology, University of Sheffield, England.
J
J
Wilkinson
L H
LH
Munro
J A
JA
Higgins
D001054:Apolipoproteins A / Q000032:analysis*; D001055:Apolipoproteins B / Q000032:analysis*; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D017270:Lipoprotein(a) / Q000097:blood; D008099:Liver / Q000737:chemistry*
D001054:Apolipoproteins A; D001055:Apolipoproteins B; D017270:Lipoprotein(a)