THE UNIVERSITY OF MANITOBA STUDIES ON OVINE PLACINTAL ...

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v¡hereas in the tissue extractr the principal component
was a species larger than M"W. 1001000. However, no such
species has been characterized in extracts from maternal
serum obta j-ned during pregnancy nor from placental tissue
during hPL purification, and other workers (Nerí et aI ,
1972¡ Genazzan i et a7, L974¡ Rahman eÈ al , 1974) reportêd
that. hPL synÈhesized by syncytiotrophoblast in tissue.
cuLture is identical to that, Ísolated from placental
tissue rúith a molecular weight of 21,600.
Synthesis of hpl by polyribosomes a¡id mRNA isol-ated
from placental tissue and incubated in vitro has been
reported. Using a cell-free system containing pl-acental
ribosomes, Krebs II ascites tumor cetl sap, and 3ss_methionine,
Boime and Boguslawski (I974al demonstrated in vitro synthesis
of hPL, which was identical by tryptic fingerprints. The
amount synthesízed represented 5g of total protein made
by early placental pol_yribosomes and l0* of that by full_
term placental polysomes. Hor¡ùever, ín a subsequent study
(Boime et a1 , J-974b), they used a specific radioimnunoassay
to neasure hPL and found that four times as much hpl was
made by tern placental ribosomes as by first-trinester
incubations. Haustraete et al (1975) estimated by incubation
with Labeled amino acids and immunoprecipitation of the
products that 7t of pept,ide synthesized on term-placental
polysomes represent, hpl,. Chatterjee et aI (1926) also
examined the in vitro translation of early and full term
pl-acental polyribosornes and obtaíned no labelled hpL at