Effect of Sodium Molybdate on Androgen Binding to Its Receptor from Shionogi Carcinoma 115
The effects of molybdate on the binding characteristics of androgen receptor from the androgen-dependent mouse tumor (Shionogi carcinoma 115) with 17/β-hydroxy-5α-androstan-3-one were studied by the charcoal adsorption method. The dissociation constant (Kd) was (4.65±0.54) ×1O－11 M in the presence of 10―12 mM sodium molybdate, which was one order of magnitude lower than the value without molybdate ((4.54±0.72)× 10－10 M). Since the half life of the binding activity of unbound receptor was extended from 10 h to 75 h by adding molybdate, the effects of chaotropic reagents on binding were studied in the presence of molybdate. KC1 (0.3 －1.0 M) remarkably increased Kd without affecting the maximuｍ binding capacity or the dissociation rate. KSCN (>0.1 M) had no effect on Kd but increased the dissociation rate, and while at concentrations at or above 0.5 M it completely inhibited the androgen binding to the cytosol receptor. Urea (0.5－2.0 M) increased Kd proportionally to the increase in the dissociation rate. Kd was also increased by 0.2－0.5 M guanidine, but the maximum binding capacity was reduced.
