The effect of a ribonuclease inhibitor from human placenta on the in vitro synthesis of human placental proteins.

Addition of a ribonuclease inhibitor (10 micrograms/ml) from human placenta caused 2-3-fold increase of [3H]leucine incorporation in the wheat germ extract as directed by human placental poly (A)-mRNA. Analysis of the translated products by sodium dodecyl sulfate/polyacrylamide gel electrophoresis/fluorography revealed that the inhibitor preferentially increased the yields of the larger proteins, particularly those of larger than Mr 40 000. In the presence of the inhibitor, yields of two placental proteins (human placental lactogen and human chorionic gonadotropin) were increased about 70-80% as detected by immunoprecipitation with specific homologous antisera. The method provided an improvement of translation system for studying biosynthesis of other human placental proteins.