Inhibitory effect of alpha-fetoprotein on protein synthesis in a reticulocyte lysate cell-free system

The inhibitory effect of human alpha-fetoprotein on the protein synthesis (incorporation of [3H]leucine into the total protein fraction) weas observed in a rabbit reticulocyte lysate cell-free system. The incorporation was inhibited to 50% of the control level by 14-16 microM alpha-fetoprotein, and decreased to about 15% at a concentration higher than 40 microM. An almost identical dose dependence was obtained between fetal alpha-fetoprotein and hepatoma-derived alpha-fetoprotein. This inhibitory effect on the protein synthesis was due to the interference of alpha-fetoprotein to the 40 S initiation complex formation from the ternary complex (eukaryotic initiation factor 2.GTP.Met-tRNAfMet). In contrast human serum albumin purified from fetal cord sera did not exhibit this inhibition under the same conditions. These results indicate that alpha-fetoprotein may function as a regulator of the protein synthesis in the fetal stage.