Journal of Lipid Research, Vol 28, 1118-1123, Copyright © 1987 by Lipid Research, Inc.
Separation and isolation of human apolipoproteins C-II, C-III0, C-III1, and C-III2 by chromatofocusing on the Fast Protein Liquid Chromatography system
MW Huff and WL Strong
Department of Medicine, University Hospital, University of Western Ontario, London, Canada.
Chromatofocusing, which separates proteins based on differences in
isoelectric point, has been used on the Fast Protein Liquid Chromatography
(FPLC) system (Pharmacia) to separate the C apolipoproteins from human very
low density lipoproteins (VLDL). Using a Mono P column (Pharmacia), a pH
gradient between pH 6.2 and pH 4.0 was generated using buffers containing 6
M urea, at a flow rate of 0.5 ml/min. Typically, runs took approximately 45
min. Chromatofocusing of delipidated whole VLDL produced sharp,
well-resolved peaks for the C apolipoproteins. However, as determined by
analytical isoelectric focusing (IEF), the apolipoprotein E isoforms were
not separated from apoC-II, and they contaminated the other apoC species to
a variable extent. In addition, apoC-II was not resolved from apoC-III0.
Preliminary precipitation of VLDL with acetone prior to delipidation
removed both apolipoproteins E and B. Using a start buffer of 25 mM
histidine, pH 6.2, and a 1:30 dilution of the polybuffer exchanger (eluting
buffer), apoC-II, C-III0, C-III1, and C-III2 were well resolved in
run-times of approximately 60 min. The C apoproteins proved to be pure by
analytical IEF and immunoassay with monospecific antisera against apoC-II
and C-III. Recovery was over 90% of the protein chromatographed. In
addition, a variant of apoC-II present in VLDL of a hypertriglyceridemic
subject was clearly resolved from the other C apolipoproteins. This
technique is superior to conventional methodology in terms of its time
saving and high resolution. The application of this technique to the study
of C apolipoprotein variants and C apolipoprotein specific radioactivity
determinations is possible.