In 18 term placentas obtained from normal pregnancies in a US urban middle class population, the DNA content averaged 1,346 mg, RNA content 1,637 mg and protein content 58.3 g. C Comparisons were made with similar determinations on placentas obtained at 10–18 weeks of pregnancy and on hydatidiform mole and choriocarcinoma tissue. Only in choriocarcinoma were DNA, RNA, and protein content per gram wet tissue higher than in either early or term placenta or in hydatidiform mole. Polysomes were obtained from these 18 placentas and their capacity to program cell-free peptide synthesis compared with that observed with polysomes from early placentas, hydatidiform mole and choriocarcinoma. In all cases, cell-free peptide synthesis was highly dependent on the state of stabilization of the polysomes and on the origin of the pH 5 protein preparation used as a source of transferring and activating enzymes. Among inhibitors of ribonuclease, only 0.5–2.0 mM EDTA stabilized the free and membrane-bound polysomes from early and term placentas. Similarly, only 3–5% bentonite stabilized polysomes from choriocarcinoma. The polysomes from hydatidiform mole showed a different pattern: their membrane-bound polysomes remained aggregated in the absence of exogenous ribonuclease inhibitors whereas their free polysomes were uniquely stabilized by 2–3% bentonite. Under optimal conditions for isolation, the polysome-monosome ratio was 3 to 1 in both normal and tumor trophoblast. Membrane-bound ribosomes accounted for 9–35% of the total ribosome complement in these preparations with the balance being free ribosomes. Rat liver pH 5 enzyme was significantly more effective in cell-free peptide synthesis than the autologous early or late placental pH 5 enzyme. When activated by rat liver pH 5 enzyme, there was a similar magnitude of 14C-peptide synthesis in cell-free systems programmed by properly stabilized polysomes obtained from early or term placentas or from tumor trophoblast.

Keywords:
Human placenta, Hydatidiform mole, Choriocarcinoma, Placental biochemistry, Placental cell-free protein synthesis
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© 1973 S. Karger AG, Basel
1973
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