A minicolumn apparatus for androgen-binding protein measurement

Human Sertoli cells in vitro: morphological features and androgen-binding protein secretion

Sertoli cells play a pivotal role in the regulation of spermatogenesis as they provide the anatomical basis of the blood-testis barrier. In the present paper we report some results of our studies on the ultrastructural features, the responsiveness to FSH, and the ability to secrete androgen-binding protein (ABP) of human Sertoli cells in vitro. The nucleus showed the characteristic foldings of the nuclear membrane, scattered chromatin, and a fibrillar nucleolus. In the cytoplasm Charcot-Boettcher crystals were present and active phagocytic activity was documented by the presence of vacuoles containing lipids and cellular debris. Human Sertoli cells in culture responded to FSH with a maximal rise in cAMP that was approx. 3-fold. This response to FSH is comparable to that reported for the adult rat but lower than that of the immature rat, and suggests that human as well as rat Sertoli cells could have a reduced response to FSH since sexual maturation was achieved. As no evidence has been reported on ABP secretion by human Sertoli cells in culture we evaluated the concentration of this protein in the Sertoli cell spent media. Human Sertoli cells in culture produced ABP and the response to FSH was dose-related. The Kd value of human ABP (hABP) was approx. 7.5 nM, being slightly higher than that of the rat ABP and an order of magnitude different from that of sex hormone-binding globulin (SHBG) present in human plasma. We also measured the association and dissociation rates of dihydrotestosterone-hABP complexes and the Kd/Ka ratio was very close to the value of Kd of the Scatchard analysis. The differences between hABP and SHBG may open the way to the selective measurement of ABP in many conditions of male infertility.

Solid-phase assay for determination of binding parameters of ligand-protein complexes with high dissociation rates

The binding parameters, the affinity constant (Ka) and binding capacity (Q), of a protein possessing ligand-protein complexes with a high dissociation rate (Sex Steroid Binding protein from Bufo arenarum) were determined using a solid-phase method. The technique is based upon the adsorption of the steroid-protein complex to DEAE-cellulose. This method was compared with a nonequilibrium method (charcoal adsorption of free ligand), and the latter resulted in underestimation of both binding parameters, Ka and Q. The solid-phase method reported here is appropriate to determine the binding parameters of proteins with high dissociation rates because the results are independent of the complex half-time. The method also possesses advantages compared to other equilibrium assays such as dialysis or steady-state electrophoresis. With minor modifications, it may be useful to characterize different proteins, particularly those possessing ligand-protein complexes with very high dissociation rates.

Partial purification of androgen binding protein from bull epididymis

An androgen binding protein (ABP), with an equilibrium dissociation constant of 4.2 nM and a molecular weight of about 100 kDa, has been purified from bull epididymal extracts using a four-step procedure. These preliminary results underline the main difficulties encountered in the purification of this protein present at a very low concentration (i.e. 50-fold less than in rat or rabbit epididymides). Ammonium sulfate precipitation is not a suitable step due to the formation, in presence of salt, of insoluble material leading to a loss of ABP. Lipids, particularly phospholipids, might be implicated in this phenomenon. Several steps, including anion exchange in batch followed by concentration, affinity chromatography and HPLC gel filtration allowed us to obtain a 7667-fold purified protein with a 9% yield.