A new assay method for the determination of oestrogen receptors.

A new assay method was developed to determine the quantity of oestrogen cytoplasmic receptors which are capable of associating with acceptor sites on chromatin. The quantity of oestrogen receptor complexes associated with chromatin is of paramount importance in the mechanism of action of oestrogen. This method is based on the specific binding properties of oestrogen to the receptor and on the binding of the complex to chromatin. Cytosol was pre-incubated with [3H]oestradiol-17 beta ([3H]Oe2) to form a complex, and further incubated with a constant amount of chromatin. After this the quantity of [3H]Oe2 cytosol receptor complexes specifically associated with the chromatin was determined. The binding activity of the chromatin to the [3H]Oe2 receptor complex was stable for at least six months in 0.15 M NaCl at -20 degrees C. This method enables us to determine the quantity of the biologically active oestrogen receptors more specifically than with other methods.