Influence of cyclic nucleotides on the processing of the carbohydrate part of the alpha-subunit of human choriogonadotropin by first trimester human placenta tissue.
In pulse-chase experiments ([35S]Met as radioactive label) 4 intracellular forms of the alpha-subunit (apparent molecular weights of 11, 16.5, 19.5, and 23.4 kDa) were observed whereas almost no label was incorporated into the beta-subunit. The 23.4 kDa form was secreted as free alpha-subunit, the others were precursors of the alpha-subunit contained in secreted human choriogonadotropin. The rate-limiting step seemed to be the processing of the 19.5 kDa precursor by alpha-mannosidase II. 8-bromo-cAMP increased the total amount of intracellular forms of the alpha-subunit and accelerated significantly the velocity of all glycosylation steps. It seemed to cause a higher efficacy of the alpha-mannosidase II reaction. In the presence of 8-bromo-cAMP intracellular as well as extracellular alpha-subunits showed a higher sialic acid content.
Hilf
G
G
Department of Biochemistry II, University of Heidelberg, F.R.G.
Merz
W E
WE
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D050260:Carbohydrate Metabolism; D046508:Culture Techniques; D000242:Cyclic AMP / Q000494:pharmacology*; D006152:Cyclic GMP / Q000494:pharmacology; D005260:Female; D015292:Glycoprotein Hormones, alpha Subunit / Q000378:metabolism*; D006031:Glycosylation; D006596:Hexosaminidases / Q000378:metabolism; D006801:Humans; D008358:Mannose / Q000032:analysis; D008361:Mannosidases / Q000378:metabolism; D008970:Molecular Weight; D019158:N-Acetylneuraminic Acid; D009439:Neuraminidase / Q000378:metabolism; D010920:Placenta / Q000378:metabolism*; D011247:Pregnancy; D014176:Protein Biosynthesis; D011498:Protein Precursors / Q000378:metabolism; D012794:Sialic Acids / Q000032:analysis; D043323:alpha-Mannosidase
D015292:Glycoprotein Hormones, alpha Subunit; D011498:Protein Precursors; D012794:Sialic Acids; D015124:8-Bromo Cyclic Adenosine Monophosphate; D000242:Cyclic AMP; D006596:Hexosaminidases; D008361:Mannosidases; D009439:Neuraminidase; D043323:alpha-Mannosidase; D019158:N-Acetylneuraminic Acid; D006152:Cyclic GMP; D008358:Mannose; D015056:1-Methyl-3-isobutylxanthine