Abstract
Addition of a ribonuclease inhibitor (10 μg/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 sodiumdodecylsulfate/polyacrylamide gel electrophoresis/fluorography revealed that the inhibitor preferentially increased the yields of the larger proteins, particularly those of larger than M r 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.