Figure 1.

Equilibrium binding of [³H]PREG to fetal brain cytosol. Charcoal-stripped cytosol samples (0.2 ml, 2.5 mg of protein per ml) were incubated with increasing concentrations of [³H]PREG in TEDG buffer, pH 8.5, at 40°C for 30 min. Bound steroid was separated by gel filtration on Sephadex LH20 at 0–4°C. Binding constants were determined with the Macintosh ligand program. B/U, bound/unbound; B, bound.