A MEMBRANE-PROTEIN ASSOCIATED WITH THE PROLACTIN RECEPTOR STUDIES WITH A PHOTOACTIVATABLE HUMAN GROWTH-HORMONE DERIVATIVE

Prolactin receptor from rat liver (PRL-R, 42 kDa) was cross-linked to a radiolabeled azidophenacyl derivative of human growth hormone ([I-12 5]AP-hGH) to yield a 63 kDa adduct. In addition, a protein of Mr 50-52 K was detected as a 73 kDa complex. Microsomes incubated with either (a) increasing amounts of [I-125]AP-hGH, or (b) a fixed amount of phot oprobe and increasing concentrations of unlabeled hGH, showed that the 73/63 kDa band intensity ratio remains constant (0.71-0.77). Once tra nsferred onto nitrocellulose membranes, only the 42 kDa protein is abl e to bind [I-125]AP-hGH or [I-125]hGH. Two anti-PRL-R monoclonal antib odies fail to cross-react with proteins of Mr 50-52 K. In membranes so lubilized with olamidopropyl)-dimethylammonio]-1-propanesulfonate (CHA PS), a significantly lower amount of the 73 kDa complex is detected. T hus, the 50-52 kDa protein appears to be structurally unrelated to, bu t is presumably associated with the PRL-R. The 73 kDa complex is also detected under low membrane fluidity conditions (1 degrees C), indicat ing that PRL-R associates to this 50-52 kDa protein prior to hormone b inding. Perfusion of rat liver with [I-125]AP-hGH shows that this asso ciated protein accompanies the receptor along its intracellular pathwa y.