Isolation and partial characterization of a pair of prolactins released in vitro by the pituitary of a cichlid fish, Oreochromis mossambicus

Authors

Jennifer L. Specker, University of Rhode Island
David S. King
Richard S. Nishioka
Kunikatsu Shirahata
Kazuo Yamaguchi
Howard A. Bern

Document Type

Article

Date of Original Version

1985

Department

Zoology

Abstract

The pituitary of the cichlid fish tilapia secretes two prolactins (PRLs) of molecular masses 20 kDa and 24 kDa. The 20-kDa PRL has an isoelectric point in the range of those of mammalian PRLs (pI 6.7), but the 24-kDa PRL is unusually basic (pI 8.7). Partial sequence information indicates that the PRLs are homologous but distinct proteins, differing by five amino acids within the first 29 NH₂-terminal residues. Homology in the known region is higher with chum salmon PRL than with known mammalian PRLs. Reversed-phase HPLC permits isolation of these two PRLs and a single tilapia growth hormone from culture medium or from the pituitary in a single step. HPLC and radio-HPLC analysis of [³H]leucine pulse-chase experiments reveal that each PRL is secreted in vitro at remarkably high rates (21 pmol per gland per hr) and that the two PRLs are released in approximately equimolar amounts, suggesting the coordinate regulation of the secretion. Both PRLs exert characteristic PRL activity in that they prevent the loss of Na⁺ from the plasma of hypophysectomized tilapia in fresh water.

Citation/Publisher Attribution

Specker, J. L., King, D. S., Nishioka, R. S., Shirahata, K., Yamaguchi, K., & Bern, H. A. (1985). Isolation and partial characterization of a pair of prolactins released in vitro by the pituitary of a cichlid fish, Oreochromis mossambicus. Proceedings of the National Academy of Sciences Nov 1985, 82(22), 7490-7494. doi: 10.1073/pnas.82.22.7490.

Available at: https://doi.org/10.1073/pnas.82.22.7490