THE UNIVERSITY OF MANITOBA STUDIES ON OVINE PLACINTAL ...

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and Biasucci (1969) denonstrated synthesis of hcc by incubating
placental tissue ln a 14c-1.bel1ed amino acid mixture and
submitting the medium after incubation to i¡rununoelectrophoresis
and autoradiography. They established that hCG synthesis was
greater in placentas from 4 to 10 \^reeks gestatiôn than in
1.4 to 18 week placentas.
The mechanism of synthesis of the peptide portion
of hCG has been explored using cell-free systems in which
polyribosomes carrying nascent. peptide chains or mRNA
extracted from these are transl-ated. Chatterjee et al (1976
and 1977) have examined the amount of hCc synthesized by the
first trimesÈer and term poi-yríbosomes prepared from human
pLacentas. The polyribosomes were incubated with tritium-
leucine, and the labelled hCG chäins were precipitated vrith
carrier hCG and anti-hCc serum. The immunoprecipitate was
resolved on SDS gels, which were then cut into small slices.
They demonstrated that there are th¡o partially resolved radioactive
peaks corresponding to peptides of MW I0,000 and 16,000,
which are the molecular weights of the alpha and beta chains
of hCG before addition of sugars. The identity of these
tr,,to peaks were confirmed by subsequenÈ experiments in which
specific antisera for each subunit of hCG !,las used.
This technique $ras used to shov¡ that hCG peptides
are predominantly synthesized on membrane-attached ribosomes,
in conformity with the pat.tern for the secreted protein (Munro
et aI, I9741 . PoLyribosomes prepared from first-trimester
placenta showed 118 of all nascent peptides to be hCG, whereas