BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS Pages 127-134 EVIDENCE FOR THE EXISTENCE OF 60NADOTROPIN RECEPTORS IN THE NUCLEI ISOLATED FROM RAT OVARY

S p e c i f i c b i n d i n g o f r a d i o l a b e l e d human c h o r i o n i c g o n a d o t r o p i n (hCG) t o n u c l e i i s o l a t e d from p s e u d o p r e g n a n t r a t o v a r i e s was s t u d i e d . I n c u b a t i o n of c u l t u r e d l u t e a l c e l l s or i s o l a t e d n u c l e i w i t h f l u o r e s c e i n i s o t h i o c y a n a t e c o n j u g a t e d hCG showed c o n c e n t r a t i o n of f l u o r e s c e n c e in t h e n u c l e a r r e g i o n . I s o l a t e d n u c l e i e x h i b i t e d s a t u r a b l e h i g h a f f i n i t y b i n d i n g of r a d i o l a b e l e d hCG w i t h an a p p a r e n t K d of 3 .42 x 10 I 0 M. The b i n d i n g was i n h i b i t e d by i n c r e a s i n g c o n c e n t r a t i o n s of u n l a b e l e d hCG. Under d i s s o c i a t i n g c o n d i t i o n s , t h e bound hCG was d i s s o c i a t e d from t h e n u c l e i . However, u n l i k e t h e p lasma membranes , t h e hCG bound t o n u c l e i was n o t d e g r a d e d b e f o r e d i s s o c i a t i o n . . R a d i o l a b e l e d hCG bound to t h e n u c l e i c o u l d a l s o be d i s s o c i a t e d by b r i e f e x p o s u r e t o MgC12 o r a c i d i c i n c u b a t i o n m e d i u m . The b o u n d hCG was n o t e x t r a c t a b l e w i t h 4M KC1 or 2% T r i t o n X-100. The a v a i l a b l e e v i d e n c e s u g g e s t t h a t n u c l e a r r e c e p t o r s a r e d i s t i n c t from p l a s ma membrane r e c e p t o r s f o r hCG.