The Cell-Free Synthesis of the Alpha Subunit of Human Chorionic Gonadotropin

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Abstract
The synthesis of the .alpha. subunit of human chorionic gonadotropin (hCG) was demonstrated in a cell-free system composed of polysomes derived from 1st trimester placenta and cell sap prepared from mouse ascites tumor cells. The in vitro synthesized proteins labeled with [35S]methionine had at least 4 tryptic peptides that co-migrated with the same peptides from authentic hCG. Sodium dodecylsulfate-polyacrylamide gel electrophoresis revealed the synthesis of a discrete protein, migrating with an apparent MW of about 17,000, which contained methionine-labeled tryptic peptides found in the .alpha. subunit. The level of radioactivity in these tryptic peptides was 5 times greater with polysomes from 1st trimester placentae than with those from term placentae. The efficiency of total protein synthesis in both cases was about the same. The decrease in blood levels of hCG after the 1st trimester is probably caused by a selective decrease in the rate of synthesis of the hormone.

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