Inhibin/activin beta-subunit monomer: isolation and characterization.

Area of Science:

• Endocrinology and Reproductive Biology
• Protein Chemistry
• Cellular Signaling

Background:

• Activin, a dimeric protein hormone, plays crucial roles in regulating various physiological processes.
• The beta A-subunit is a key component of activin, forming dimers like activin-A.
• Understanding the monomeric form's presence and activity is essential for a complete picture of activin function.

Purpose of the Study:

• To isolate and characterize activin immunoactivity from bovine follicular fluid and human recombinant inhibin side-fractions.
• To determine the molecular forms, relative abundance, and biological activity of activin beta A-subunit monomers and dimers.

Main Methods:

• Immunoassays (RIA) to monitor activin immunoactivity.
• Protein purification techniques including dye affinity chromatography, hydrophobic interaction, gel permeation, and reverse-phase HPLC.
• Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) for molecular mass determination.
• Cell-based assays using rat pituitary cells and thymocytes to assess biological activity.

Main Results:

• Two forms of activin immunoactivity were isolated, corresponding to a 25-kDa dimer (activin-A) and a 15-kDa monomer of the beta A-subunit.
• The beta A-subunit monomer was found in bovine follicular fluid at 25-60% the concentration of the dimer.
• In vitro, the monomer exhibited 18-45% of the dimer's activity in stimulating FSH release and suppressing thymidine uptake.

Conclusions:

• The beta A-subunit exists as both monomer and dimer (activin-A) in biological fluids.
• The monomer displays biological activity comparable to the dimer, albeit at a reduced level.
• Further investigation is needed to ascertain if monomer dimerization is required for full biological function.