Studies on dissociation of mouse prolactin from mouse hepatic receptors

The influence of pH, temperature, ethylene glycol, urea, chaotropic anions and excess unlabelled secreted mouse prolactin (smPRL) on the dissociation kinetics of 125I-iodosmPRL from mouse hepatic receptors was investigated. The destabilization of smPRL-receptor complexes by chaotropic anions followed the typical trend of the Hofmeister series: I- greater than Br- greater than Cl- greater than F-. Increasing the temperature of the dissociation reaction from 8 degrees C to 23 degrees C and 30 degrees C caused partial dissociation of 125I-iodosmPRL-receptor complexes. Dissociation of 125I-iodosmPRL from mouse hepatic receptors was pH dependent, with the slowest rate of dissociation occurring at pH 8 and the fastest rate of dissociation occurring at pH 5 and 6. Both ethylene glycol and urea accelerated the rate of dissociation of 125I-iodosmPRL from mouse hepatic receptors in a concentration-dependent manner. Dissociation of 125I-iodosmPRL from mouse hepatic receptors was 6-fold faster in the presence of excess unlabelled smPRL than in its absence. The results of these investigations suggest that both protonation/de-protonation reactions and hydrophobic interactions play important roles in stabilizing the smPRL-receptor complex. In addition, they suggest that cooperative interactions may be involved in the binding of smPRL to mouse hepatic receptors.