Studies on the dissociation of prolactin from mammary tumor membranes

The dissociation of [125I]iodo-PRL from crude membrane preparations of two transplantable rat mammary carcinomas was studied. At least 1/2 of the specifically bound PRL remains undissociated when membrane pellets are resuspended in buffer. The apparent irreversibly bound fraction can be removed at least partially upon incubation with 6 M urea, but not with 1 M urea. By all the criteria used, the dissociated PRL was undamaged. The physiological importance of this phenomenon may relate to the presence of more than one type of binding site which current techniques do not allow us to distinguish.