Evidence for an androgen binding component in human placental cytosol

Abstract

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 K d of 2.73 ± 1.25 × 10 −9 M and a concentration of binding sites of 157 ± 73 fmol/mg protein ( N = 20). In competitive binding studies, R1881, T, 5αT, 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”.