Isolation, purification, and characterization of deer mouse (Peromyscus maniculatus bairdii) prolactin

Prolactin (PRL) secreted by Peromyscus maniculatus bairdii anterior pituitaries was purified by gel filtration on Sephadex G-100 and ion-exchange chromatography on DEAE-cellulose. Peromyscus PRL (pmPRL) eluted from Sephadex G-100 with an elution-to-void volume ratio of 1.9 and at a salt concentration of 100 mM NaCl on DEAE-cellulose. Electrophoretic homogeneity of the hormone was demonstrated in several gel systems. On 7 1/2% alkaline polyacrylamide gels, pmPRL migrated with an Rf of 0.65. The molecular weight of pmPRL was estimated at 24,000 to 26,000 by sodium dodecyl sulfate electrophoresis and molecular exclusion chromatography. The amino acid composition of pmPRL was similar to other mammalian PRLs including two tryptophan residues and three disulfide bonds. Leucine was found to be the NH2-terminal residue. Circular dichroism (CD) spectra indicated an alpha-helix content of 55 +/- 5%, a value typical for prolactin molecules. However, in the region of side-chain absorption, the CD spectrum displayed a weak, asymmetric, negative band near 299 nm, with the CD returning to slightly positive values at 292 nm. This CD pattern is not typical of other secreted or stored prolactins. In the pigeon crop-sac assay, pmPRL showed a prolactin-like activity of 21 IU/mg.