Isolation and characterization of Japanese eel prolactins

Area of Science:

• Endocrinology
• Comparative Physiology
• Biochemistry

Background:

• Prolactin (PRL) is a crucial hormone regulating various physiological processes in vertebrates.
• Understanding species-specific PRL functions and structures is vital for comparative endocrinology.

Purpose of the Study:

• To isolate and characterize prolactin from the Japanese eel (Anguilla japonica).
• To investigate the biological activity and structural homology of eel prolactin variants.

Main Methods:

• Purification of eel prolactin using acid-acetone extraction, gel filtration (Sephadex G-75), and reversed-phase HPLC.
• Separation and isolation of two prolactin variants (ePRL I and II) using HPLC.
• Assessment of PRL activity by measuring plasma sodium retention in hypophysectomized killifish.
• Characterization of PRL properties including molecular weight (SDS-PAGE), isoelectric point (gel electrofocusing), and N-terminal residue analysis.
• Amino acid composition and partial sequencing for homology studies.

Main Results:

• Two distinct prolactin variants, ePRL I and II, were successfully isolated from Japanese eel pituitary glands.
• Both ePRL I and II demonstrated equipotent activity in maintaining plasma sodium levels in killifish adapted to freshwater.
• The purified eel prolactins exhibited a molecular weight of 22 kDa and an isoelectric point of 10.1.
• Amino acid analysis revealed high homology between ePRL I and II, and a closer relationship to teleostean PRLs compared to mammalian PRLs.

Conclusions:

• The Japanese eel possesses at least two prolactin variants with conserved osmoregulatory functions.
• The structural characteristics of eel prolactin align more closely with those of other fish, highlighting evolutionary divergence.
• This study provides valuable insights into the structure-function relationship and evolution of prolactin in fish.