Mechanism of prolactin action on the dissociation of prolactin from rabbit mammary gland receptor.

In order to elucidate the action of prolactin (PRL) on the dissociation of PRL from the receptor, Triton-solubilized and concanavalin A-purified rabbit mammary gland PRL receptor was immobilized onto a nitrocellulose membrane, and the dissociation of PRL was determined in the presence of PRL. PRL accelerated the dissociation of PRL in a concentration dependent manner for the first 3 h of incubation. The effects of PRL on dissociation were independent of the occupancy of PRL at the zero-time dissociation. In particular, PRL-dependency was influenced by the PRL-binding capacity of the membrane. The dissociation reaction was PRL-independent in the low-binding capacity membrane, indicating that PRL itself had no accelerating actions. With greater binding capacity, the dissociation reaction was seen to become PRL-dependent. It was concluded that PRL accelerated the dissociation of PRL through the formation of PRL-receptor complex when the receptor was located closely to the neighboring receptors.