[The ionic heterogeneity of human prolactin (PRL) from amniotic fluid]

The ionic heterogeneity of prolactin (PRL) secreted in the human amniotic fluid was investigated using new precise chemical techniques. From five liters of amniotic fluid, the PRL fractions were purified with 70% ammonium sulfate precipitation, ethanol fractionation, desalting by gel filtration on Sephadex G-25, and ion-exchange chromatography using Mono Q on Fast Protein Liquid Chromatography (FPLC). The last FPLC was repeated until homogeneous preparations were obtained. Hormonal activity of each fraction was determined with a NIADDK radioimmunoassay (RIA) kit for human PRL. The PRL activity of the finally-purified component was also assayed by radioreceptor analysis (RRA) using rat liver cell membranes as the receptor. From the amniotic fluid, seven components of the PRL were eluted at NaCl concentrations from 0.065M to 0.13M in 0.02M Tris-HCl, pH 8.0. The RRA/RIA values of these seven components were different from each other (from 0.32 to 0.97). The lower the NaCl concentrations, the higher the RRA/RIA values were. The molecular weight of each component determined by gel filtration on TSK-SW 3000 with HPLC, was similar (MW 23,000) corresponding to "small-PRL".