Evidence for an androgen binding component in human placental cytosol

A high-affinity, low-capacity androgen binding component is present in human term placental cytosol. A synthetic androgen tracer, [3H]-R1881, was bound by a single class of binding sites with a K4 of 2.73 +/- 1.25 X 10(-9) M and a concentration of binding sites of 157 +/- 73 fmol/mg protein (N = 20). In competitive binding studies, R1881, T, 5 alpha T, androstenedione and DHEA, were active competitors, but not estradiol, progesterone or cortisol. The [3H]-R1881 macromolecule complex exhibited a sedimentation coefficient of 4-5 S under low and high salt conditions, and the radioactive tracer was displaced by a 100-fold excess of unlabelled R1881. This binding component has characteristics of high-affinity, low-capacity, sedimentation behaviour and specificity, commonly attributed to androgen "receptors".