Intracellular immature subunits of human chorionic gonadotropin in first trimester placental cells: purification and characterization.
As we previously reported [Sakakibara et al. (1986) Biochem. Biophys. Res. Commun. 137, 443-452; and Tominaga et al. (1989) J. Biochem. 105, 992-997], subunits of human chorionic gonadotropin (hCG) containing immature N-linked sugar chains (immature subunits), i.e., the 21 kDa form of alpha-subunit and the 23 and 19 kDa forms of beta-subunit, are present predominantly in first trimester placental cells. The molecular mass of intracellular hCG consisting of these subunits, based on gel filtration, was approximately 200 kDa, suggesting homo- or hetero-oligomerization of intracellular hCG. In the present study, we purified the 21 kDa form of alpha-subunit as well as the 23 and 19 kDa forms of beta-subunit from fresh normal first trimester placental tissues by gel filtration and reverse-phase high-performance liquid chromatography. Purified subunits were hydrolyzed (with a decrease in their molecular weighs) by endoglycosidase H and alpha-mannosidase but not by sialidase or sialidase followed by O-glycanase, indicating that those forms have presumably only high-mannose-type N-linked sugar chains but not O-linked sugar chains of the type present in mature beta-subunit. Fifteen cycles of Edman degradation of the purified forms of the subunits were performed. Only one phenylthiohydantoin amino acid, which was the same amino acid as in the urinary beta-subunit, was detected at each step for the mixture of 23 and 19 kDa forms of beta-subunit, indicating that the protein backbones of both forms are identical to each other as well as to the urinary beta-subunit.(ABSTRACT TRUNCATED AT 250 WORDS)
Tominaga
N
N
Department of Biochemistry, School of Clinical Pharmaceutical Sciences, Nagasaki University.
Sakakibara
R
R
Shimojo
M
M
Ishiguro
M
M
D000595:Amino Acid Sequence; D002240:Carbohydrate Sequence; D006063:Chorionic Gonadotropin / Q000737:chemistry / Q000302:isolation & purification*; D002850:Chromatography, Gel; D005260:Female; D006026:Glycoside Hydrolases; D006801:Humans; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010920:Placenta / Q000737:chemistry*; D011247:Pregnancy; D011487:Protein Conformation
D006063:Chorionic Gonadotropin; D006026:Glycoside Hydrolases