Subcellular localization of intracellular forms of human chorionic gonadotropin in first trimester placenta.
To determine the subcellular sites for synthesis and processing of human chorionic gonadotropin subunits in cells, first trimester placental cells were fractionated subcellularly on sucrose density gradients. Analysis of the subcellular fractions by immunobinding techniques revealed that the rough endoplasmic reticulum-rich fraction contained only intermediates having high-mannose oligosaccharides, but the Golgi-rich fraction contained not only intermediates but also mature forms which were resistant to endoglycosidase H but sensitive to neuraminidase. These results show that human chorionic gonadotropin subunits are synthesized in the rough endoplasmic reticulum as forms containing high-mannose oligosaccharides, and their maturation occurs in the Golgi apparatus by trimming with endogenous glycosidases. They are then modified by addition of complex oligosaccharides and terminal sialic acid through glycosyltransferases.
D000118:Acetylglucosaminidase / Q000378:metabolism; D002458:Cell Fractionation; D002499:Centrifugation, Density Gradient; D006063:Chorionic Gonadotropin / Q000378:metabolism*; D018997:Chorionic Gonadotropin, beta Subunit, Human; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005260:Female; D015292:Glycoprotein Hormones, alpha Subunit; D006056:Golgi Apparatus / Q000378:metabolism; D006801:Humans; D017038:Mannosyl-Glycoprotein Endo-beta-N-Acetylglucosaminidase; D009251:NADPH-Ferrihemoprotein Reductase / Q000378:metabolism; D009439:Neuraminidase / Q000378:metabolism; D010446:Peptide Fragments / Q000378:metabolism; D010908:Pituitary Hormones, Anterior / Q000378:metabolism; D010920:Placenta / Q000378:metabolism / Q000648:ultrastructure*; D011247:Pregnancy
D006063:Chorionic Gonadotropin; D018997:Chorionic Gonadotropin, beta Subunit, Human; D015292:Glycoprotein Hormones, alpha Subunit; D010446:Peptide Fragments; D010908:Pituitary Hormones, Anterior; D009251:NADPH-Ferrihemoprotein Reductase; D009439:Neuraminidase; D000118:Acetylglucosaminidase; D017038:Mannosyl-Glycoprotein Endo-beta-N-Acetylglucosaminidase