Steroidogenic Activity of Synthetic Hybrid Molecules Composed of Human Chorionic Gonadotropin and Either the A or B Chain of Lectin Ricin or Horseradish Peroxidase
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概要
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Human chorionic gonadotropin (hCG) is a glycoprotein consisting of noncovalently bound α- and β-subunits which shows hormonal activity (stimulatory effect on testosterone production) toward rat Leydig cells. To modify the hormonal activity of hCG, hybrid molecules composed of hCG and other glycoproteins, either the A or B chain of lectin ricin (hCG-A and hCG-B) through disulfide bridges and horseradish peroxidase (hCG-HRP) through Schiff's base, were synthesized. Hormonal activity and the effect of these hybrids on [^<125>I]hCG binding to rat Leydig cells were compared to those of native hCG. Modification of hCG resulted in a significant decrease in hormonal activity for hCG-HRP but not for hCG-A to aproximately 1/100 and 1/10 that of native hCG, respectively. On the other hand, hCG-B unexpectedly showed hormonal activity similar to that of native hCG. These hybrids inhibited the binding of ^<125>I-labeled hCG to rat Leydig cells with potencies of 1/10,1/100 and 1/500 that of hCG for hCG-B, hCG-A and hCG-HRP, respectively. These results indicate that the B chain of ricin, the active component hCG-B, participated in stimulating testosterone production according to its own nature. Data which indicate that hybrids consisting of hCG subunits and the B chain of ricin (α-B and β-B) stimulated testosterone significantly more than hybrids consisting of hCG subunits and A chain (α-A and β-A) support the above finding. When asialofetuin was added to the assay system as an inhibitor of binding of the B chain to galactose residues attached to the cell surface membrane, the inhibition of hCG-B with the binding of [^<125>I]hCG to rat Leydig cells was depressed and testosterone production provoked by hCG-B was repressed to the level induced by hCG-A. Furthermore, a hybrid consisting of hCG and enzymatically deglycosylated B chain stimulated testosterone production, but its activity was significantly weaker than that of hCG-B with the level approaching that of hCG-HRP. These results suggested that three kinds of binding of hCG-B to rat Leydig cells participate in expression of hormonal activity of hCG-B as follows : (1) binding of the hCG moiety to its receptor, (2) binding of the B chain moiety, as lectin, to terminal galactose residues attached to cell-surface membrane, and (3) binding of a lectin-like protein(s) in the cell-surface membrane to oligosaccharides of the B chain moiety.
- 社団法人日本薬学会の論文
- 1991-11-25
著者
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境 晶子
Department Of Biochemistry School Of Clinical Pharmaceutical Sciences Nagasaki University
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榊原 隆三
長崎大・薬
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石黒 正恒
Department of Biochemistry, School of Clinical Pharmaceutical Sciences, Nagasaki University
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榊原 隆三
Department of Biochemistry, School of Clinical Pharmaceutical Sciences, Nagasaki University
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石黒 正恒
長崎大学薬学部
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大脇 健二
Department of Biochemistry, School of Clinical Pharmaceutical Sciences, Nagasaki University
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石黒 正恒
Department Of Biochemistry School Of Pharmaceutical Sciences Nagasaki University
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大脇 健二
Department Of Biochemistry School Of Clinical Pharmaceutical Sciences Nagasaki University
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Ishiguro Masatsune
Department Of Biochemistry School Of Clinical Pharmaceutical Sciences Nagasaki University
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Ishiguro Masatsune
Department Of Biochemistry School Of Clinical Pharmaceutical Science Nagasaki University
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