JBC, Vol. 252, Issue 6, 2046-2053, Mar, 1977
Biosynthesis of ferritin in rat hepatoma cells and rat livers. I. Synthesis and assembly of protein subunits of ferritin
S. S. Lee and G. W. Richter
Cell fractions were prepared from ACI rat livers and from rat hepatoma cell
clone M-5123-C1. Radioimmunoassays of ferritin and of its protein subunits
in various cell fractions after biosynthetic labeling with [14C]leucine
were done by means of ferritin-specific and subunit-specific rabbit
antibody. In both ACI rat livers and M-5123-C1 hepatoma cells free
polyribosomes synthesized approximately 81% of the protein subunits of
ferritin, and membrane-bound polyribosomes synthesized the rest. In both
polyribosomal fractions, [14C]leucine-labeled subunits were detected
earlier than [14C]leucine-labeled ferritin and apoferritin (5 min as
against 30 min after initiation of a pulse). Time sequence studies of the
shifts of biosynthetically labeled subunits and ferritin through different
cell compartments provided evidence for vectorial transport of subunits and
of ferritin, the direction of transport being from the two polyribosomal
systems to the smooth membrane compartment and to the cytosol.