Cell-free synthesis of alpha and beta subunits of human chorionic gonadotrophin with polyribosomes from early placenta

Maruo, T.; Koide, S.S.

Acta Endocrinologica 95(1): 90-96

1980


ISSN/ISBN: 0001-5598
PMID: 6161507
Accession: 004891961

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Abstract
Polyribosomes were prepared from first trimester human placenta and assayed for protein synthetic activity in the cell-free translatory system derived from wheat germ or from first trimester placental tissue. High incorporation of , .alpha.- and .beta.-subunit and analyzed by electrophoresis on sodium dodecyl sulfate-polyacrylamide gels. The apparent MW of the immunoprecipitable CG-.alpha.-protein was estimated to be 15,000 daltons, while that of the immunoprecipitable .beta.-protein was about 24,000 daltons. Since the MW of the polypeptide part of authentic .alpha.- and .beta.-subunits are 10,200 and 16,000 daltons, respectively, the cell-free products may represent their precursor protein forms; pre-CG-.alpha. and pre-CG-.beta. The rates of production of hCG, .alpha.- and .beta.-proteins by in vitro incubation of placental polyribosomes with the wheat germ translating system were determined by the respective homologous radioimmunoassays. It is noteworthy that CG-.beta.-protein production was highest during the initial 15 min of incubation and became limited subsequently, whereas an increase in hCG and .alpha.-protein formation was observed at 90 min of incubation. The present results suggest that the placental polyribosomes contain mRNA for .alpha.- and .beta.-subunits. Earlier accelerated synthesis of CG-.beta. protein might be required for the subsequent association with the newly synthesized .alpha.-subunit protein to form hCG.