Journal of Lipid Research, Vol 16, 367-378, Copyright © 1975 by Lipid Research, Inc.
Studies on the metabolism of rat serum very low density apolipoprotein
N Fidge and P Poulis
There was a rapid transfer of radioactive peptides to other lipoprotein
fractions during the first 30 min after the intravenous injection of
125I-labeled rat very low density lipoprotein (VLDL) into rats. After this
initial redistribution of radioactivity, label disappeared slowly from all
lipoprotein fractions. The disappearance of 125I-labeled human VLDL
injected into rats was the same as that of rat VLDL. Most of the
radioactivity transferred from VLDL to low density (LDL) and high density
(HDL) lipoproteins was associated with two peptides, identified in these
studies by polyacrylamide gel electrophoresis as zone IVa and IVb peptides
(fast-migrating peptides, possibly analogous to some human C
apolipoproteins), although radioactivity initially associated with zone I
(analogous to human apolipoprotein B) and zone III (not characterized) was
also transferred to LDL and HDL. That the transfer of label from VLDL to
LDL and HDL primarily involved small molecular weight peptides was
confirmed in studies using VLDL predominantly labeled in these peptides by
in vitro transfer from 125I-labeled HDL. Both zone I and zone IV
radioactivity was rapidly removed from VLDL during the first 5 min after
injection. However, although most of the zone IV radioactivity was
recovered in LDL and HDL, only 12% of the label lost from zone I of VLDL
was recovered in other lipoproteins, with the remainder presumably having
been cleared from the plasma compartment. We have concluded that, during
catabolism of rat VLDL apoprotein, there is a rapid transfer of small
molecular weight peptides to both LDL and HDL. During the catabolic
process, most of the VLDL is rapidly removed from the circulation, with
only a small portion being transformed into LDL molecules.
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