Electrophoretic separation of prolactin secreted from mouse pituitary glands in vitro

Prolactin secreted from the mouse pituitary gland in organ culture was characterized after disc or SDS-polyacrylamide gel electrophoresis. Some pituitary glands were cultured with 3H-labelled leucine for 24 h to obtain radioactive prolactin. In disc electrophoresis, immunoreactive, receptor-bindable and 3H-incorporated prolactins formed a single band with the same relative mobility (0.5). Prolactin migrating at Rf = 0.5 was extracted and re-analysed by SDS electrophoresis. A single stained and radioactive band was observed at the same position with an apparent molecular weight of 23 000 regardless of denaturing in the presence of absence of dithiothreitol. No other band was detected. These results indicate that mouse prolactin synthesized and secreted in organ culture is homogeneous and that mouse prolactin is a single-chain molecule.