Saturation binding of [3H]oestradiol has been determined using exchange conditions, on nuclei from DMBA tumours from rats treated prior to sacrifice with oestradiol and tamoxifen alone or in combination. Application of a model to the binding data. enabled the amounts (C2) and apparent dissociation constants (Kdapp) of a second lower affinity binding component to be determined as well as the amount of a higher affinity site (C1) and its dissociation constant (K1). Kdappdid not change significantly with any pretreatment but 2 h after oestradiol (5μg) and after tamoxifen alone there was a significant decrease in Kdcompared with control. It is suggested that the difference in Kdof the higher affinity binding sites in control and 2 h oestradiol treated animals may be due to the loss of an essential co-factor, possibly cytosolic, when nuclei are isolated in the absence of ligand. © 1988.
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