Journal of Lipid Research, Vol 26, 970-976, Copyright © 1985 by Lipid Research, Inc.
Distribution of apolipoprotein A-IV among lipoprotein subclasses in rat serum
GM Dallinga-Thie, PH Groot and A van Tol
The distribution of apolipoproteins (apo) A-I, A-IV, and E in sera of fed
and fasted rats was studied using various methods for the isolation of
lipoproteins. Serum concentrations of apoA-I and apoA-IV decreased
significantly during fasting (16 and 31%, respectively), while apoE
concentrations remained essentially the same. Chromatography of sera on 6%
agarose columns showed that apoA-IV is present on HDL and as so- called
"free" apoA-IV. The concentration of "free" apoA-IV decreased six- to
seven-fold during fasting, explaining the decrease in total serum apoA-IV.
Serum apoA-I and apoE are almost exclusively associated with HDL-sized
particles. When sera are centrifuged at a density of 1.21 g/ml, marked
quantities of apoA-I (8-9%) and apoE (11-22%) are recovered in the
"lipoprotein-deficient" infranatant, suggesting that ultracentrifugation
affects the integrity of serum HDL. The nature of the chromatographically
separated carriers of serum apoA-IV was investigated by quantitative
immunoprecipitation. From these studies, it is concluded that apoA-IV in
rat serum is present in at least three fractions: 1) particles with the
size and composition of HDL, containing both apoA-I and apoA-IV and
possibly minor quantities of apoE; 2) HDL-sized particles containing
apoA-IV, but no apoA-I or apoE; 3) "free" apoA-IV probably containing small
amounts of bound cholesterol and phospholipid.