Characterization of the testicular binding site for iodinated rat FSH in the turtle, Chrysemys picta.
1. To correlate the morphological observations with the known gonadotropic activity of FSH in the turtle testis, studies of the binding of iodinated FSH were conducted. 2. These demonstrated the presence of gonadotropin-binding sites of high affinity (apparent Kd = 10(-10) M) for [125I]rFSH in turtle testicular membrane preparations. 3. Although these sites did not bind iodinated human LH or avian LH, these hormones, as well as PMSG and FSH, were effective competitive inhibitors of the binding of the radioligand. 4. Binding of the radioligand to the testis was influenced by duration of incubation and temperature. 5. Binding activity was lost after incubation with proteolytic enzymes (trypsin, pronase) but not with DNAase, lipase, collagenase and neuraminidase. 6. The binding exhibited target organ specificity (no binding observed in brain, epididymis, lung, muscle and pancreas). 7. In addition, the number of binding sites varied according to the stage spermatogenesis, being highest when the tubules contained spermatocytes and spermatids, intermediate when the tubules consisted to Sertoli cells and spermatogonia and lowest st spermiation.
Dubois
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Department of Biology, Boston University, Boston, MA 02215, USA.
Callard
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IP
D000818:Animals; D001665:Binding Sites; D017364:Collagenases; D003851:Deoxyribonucleases; D005640:Follicle Stimulating Hormone / Q000378:metabolism*; D006801:Humans; D007457:Iodine Radioisotopes; D008049:Lipase; D008297:Male; D051381:Rats; D011962:Receptors, FSH / Q000378:metabolism*; D012621:Seasons; D013091:Spermatogenesis; D013737:Testis / Q000378:metabolism*; D014357:Trypsin; D014426:Turtles / Q000378:metabolism*
D007457:Iodine Radioisotopes; D011962:Receptors, FSH; D005640:Follicle Stimulating Hormone; D003851:Deoxyribonucleases; D008049:Lipase; D014357:Trypsin; D017364:Collagenases