pH dependence of dissociation of the ovine prolactin rabbit mammary receptor complex

Ovine prolactin specifically bound to rabbit mammary membrane prolactin receptor was rapidly dissociated in a pH dependent manner with 0.1M ammonium acetate. Up to 75% of the bound hormone was dissociated at pH 4.0 or lower in less than 5 minutes. The pK of the dissociation was 4.7, implicating one or more critical carboxyl groups. Exposure of the membrane bound receptor to the dissociating buffer for up to one hour did not reduce its ability to bind hormone. The dissociated hormone was characterized as intact ovine prolactin by Bio-Gel P-150 gel chromatography and by its ability to bind to fresh rabbit prolactin receptor with the same binding affinity as native hormone.