Journal of Lipid Research, Vol 16, 1-6, Copyright © 1975 by Lipid Research, Inc.
In vitro labeling of beta-apolipoprotein with 3H or 14C and preliminary application to turnover studies
VK Murthy, TC Monchesky and G Steiner
3-H- or 14-C-labeled methyl groups were introduced into apolipoproteins of
human and pig low density lipoproteins (LDL). 98% of the label was
recovered in the apoprotein of radiomethylated LDL. Such methylated
lipoprotein was compared with the corresponding unlabeled LDL with respect
to its electrophoretic and immunochemical properties, and its behavior in
the analytical ultracentrifuge. The data demonstrated that neither the
human nor pig LDL underwent gross changes as a result of methylation. The
applicability of radiomethylated pig LDL as a tracer for studying the
turnover of LDL in pigs was examined. The results showed that the behavior
of unscreened and screened 3-H-labeled LDL was similar. The LDL disappeared
with an initial t1/2 of 1.1 hr and a later t1/2 of 30 hr. These values
agreed well with those reported for radioiodinated LDL. The technique of
radiomethylation of lipoprotein may afford an advantage over
radioiodination as it may label peptides that do not have tyrosine.
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