Prolactin receptors in tilapia (Sarotherodon mossambicus) tissues: binding studies using 125I-labeled ovine prolactin.

The binding of 125I-labeled ovine prolactin (oPRL) to membrane preparations of tissue from freshwater-adapted tilapia (Sarotherodon mossambicus) was examined. Liver, ovary, and testis showed a relatively high specific binding (5-10%). A lower specific binding occurred consistently in intestine and gill tissue, and inconsistently in urinary bladder and kidney preparations. Desaturation experiments with MgCl2 indicated that a majority of the PRL receptors were already occupied by endogenous PRL. Scatchard analysis of liver binding gave a dissociation constant of 0.6 X 10(-9) M and a capacity of 207 fmol/mg protein.