Immature human chorionic gonadotropin (hCG) in first trimester placental cells is bound to an ATP-binding protein forming high-molecular-weight hCG.
Human chorionic gonadotropin (hCG) in first trimester placental cells is made up of immature alpha- and beta-subunits containing only N-linked high-mannose sugar chains, which are of 21 kDa for the alpha-subunit and 23 and 19 kDa for the beta-subunit. However, the apparent molecular weight of immature hCG from placental cell extracts has been estimated from gel filtration to be much higher (100-200 kDa; high molecular weight-hCG, HMW-hCG) based on gel filtration than the theoretical value (approximately 44 kDa) of the alpha beta dimer (alpha beta-hCG). We prepared a gel-filtered fraction containing HMW-hCG and investigated treatments for converting it to alpha beta-hCG. We found that the molecular weight of HMW-hCG was decreased to close to that of alpha beta-hCG by treatment with acetone, proteases, or chelating agents. These treatments also shifted the isoelectric point of HMW-hCG from the acidic region (pI = 4-6) to the alkaline (pI = 9-11), approximating to that of alpha beta-hCG. We also found that HMW-hCG, but not acetone-treated HMW-hCG, bound to ATP-agarose resin. These results suggested that the immature alpha beta-hCG molecule in placental cells may be bound to an acidic ATP-binding protein to form HMW-hCG.
Shimojo
M
M
Department of Biochemistry, School of Clinical Pharmaceutical Sciences, Nagasaki University.
Sakakibara
R
R
Ishiguro
M
M
D000096:Acetone / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D002614:Chelating Agents / Q000494:pharmacology; D006063:Chorionic Gonadotropin / Q000737:chemistry / Q000378:metabolism*; D002846:Chromatography, Affinity; D002850:Chromatography, Gel; D010450:Endopeptidases / Q000494:pharmacology; D005260:Female; D006801:Humans; D015151:Immunoblotting; D007526:Isoelectric Point; D008970:Molecular Weight; D010920:Placenta / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D013055:Spectrophotometry, Infrared
D002352:Carrier Proteins; D002614:Chelating Agents; D006063:Chorionic Gonadotropin; D000096:Acetone; D000255:Adenosine Triphosphate; D010450:Endopeptidases