Photoaffinity labelled rat androgen-binding protein and human sex hormone steroid-binding protein bind specifically to rat germ cells.
A specific receptor with high affinity for rat androgen-binding protein (rABP) was identified in isolated adult rat germ cells and in the corresponding plasma membrane-enriched preparations. Binding was reversible and time-dependent, with maximum relative binding after 40 min at 4 degrees C; it was pH-dependent, with maximum binding at pH 6-8. Unlabelled rABP and human sex steroid-binding protein (hSBP), but not lactotransferrin, serotransferrin, asialofetuin, fetuin or bovine serum albumin, competed with labelled rABP for binding sites on isolated germ cells. Scatchard analysis revealed a single class of binding site with apparent dissociation constant (Kd) values of 0.78 +/- 0.04 nM and 0.97 +/- 0.05 nM in intact germ cells and plasma membrane preparations respectively. A Kd of 1.72 +/- 0.12 nM for hSBP showed that the receptor binding site was effective for both androgen-carrier molecules. Labelled rABP incubated with solubilized germ cell membrane fractions at pH 7 formed a complex excluded from Superose 6B mini-gels; this complex was not formed at pH 3. The receptor complex was also abolished in the presence of a 100-fold excess of either unlabelled rABP or unlabelled hSBP, or in the presence of 20 mM EDTA. These results suggest that the plasma membrane of rat germ cells contains a receptor which selectively binds rABP and hSBP.
Felden
F
F
Laboratoire de Biochimie Nutritionnelle, INSERM U 308, Faculté de Médecine, Université de Nancy I, Vandoeuvre-lès-Nancy, France.
Guéant
J L
JL
Ennya
A
A
Gérard
A
A
Frémont
S
S
Nicolas
J P
JP
Gérard
H
H
D000345:Affinity Labels; D000727:Androgen-Binding Protein / Q000378:metabolism*; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D002850:Chromatography, Gel; D005854:Germ Cells / Q000378:metabolism*; D006801:Humans; D008297:Male; D010777:Photochemistry; D051381:Rats; D011919:Rats, Inbred Strains; D012738:Sex Hormone-Binding Globulin / Q000378:metabolism*; D013379:Substrate Specificity
D000345:Affinity Labels; D000727:Androgen-Binding Protein; D012738:Sex Hormone-Binding Globulin