| Research Abstract |
In order to study structure and hormonal function relationship of human chorionic gonado tropin (hCG), hCG (alpha beta) was chemically coupled to ricin A or B chain via S-S bridge. These hybrids, when incubated with rat Leydig cells, could stimulate the production of testosterone accompanied by stimulative increase of cellular cAMP. From the binding study and toxic action of hybrids, it was concluded that these hybrids were first bound to hCG.receptor(s) on the cell surface, then internalized, and finally expressed their hormonal and toxic action. When ratios of ED_<50> for stimulation of cAMP and testosterone were compared, a surprising and new result was obtained that hybrids-required less amount of cAMP than hCG did for the submaximal production of testosterone, suggesting an another second messenger may play a role in the signal transduction of hCG. Effects of protein kinase A inhibitors, and the contribution of catecholamine receptors have also explored. In addition, examination of hormonal action of other hybrids, hCG-HRP,alpha-A, alpha-B, beta-A, beta-B, have shown that all exhibited stimulative testosterone production in different degree with a concomitant increase of cAMP. Furthermore, hybrids containing B chain were found to be more potent hormone analog than the others.
From these results, it was concluded in the rat Leydig cells that
(1) only a small amount of cAMP was necessary, whereas no inositol phosphate/protein kinase C nor Ca^<++> may not participate in the hCG action, and
(2) hCG should interact with at least three places on the cell surface, hCG receptor, membrane glycoprotein possessing-terminal galactosyl residues,lftnd a lectin which recognizes high-mannose type oligosaccharide chain of hCG.
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