Conformational studies of secreted mouse pituitary prolactin.

A secreted form of mouse pituitary prolactin has been shown to contain only a single tryptophan residue. All previously reported prolactins contain two tryptophans. Circular dichroism spectra indicate that secreted mouse prolactin is conformationally similar to stored forms of prolactin previously isolated from several other species, including its alpha-helix content (65%). However, like secreted rat prolactin, secreted mouse prolactin shows no tryptophan signal in its circular dichroism spectrum. All stored forms of prolactin studied to date display distinct tryptophan signals. This suggests the possibility that secretion of prolactin may be accompanied by modification of the protein's tertiary structure.