The putative molybdate-stabilized progesterone receptor subunit is not a steroid-binding protein

Area of Science:

• Biochemistry
• Molecular Biology
• Endocrinology

Background:

• Recent reports suggest a different identity for the chick progesterone receptor.
• Puri et al. identified an 88,000 molecular weight protein as the non-transformed, molybdate-stabilized receptor.

Purpose of the Study:

• To investigate the discrepancy in chick progesterone receptor characterization.
• To re-evaluate the identity of the 88,000 molecular weight protein reported by Puri et al.

Main Methods:

• Replication of Puri et al.'s methods for protein isolation.
• Analysis of the 88,000 molecular weight protein using tryptic mapping and DEAE-Sephadex A-25 chromatography.
• Assessment of progesterone-binding affinity and biospecificity of elution from affinity resins.

Main Results:

• The 88,000 molecular weight protein was obtained in a 10-fold molar excess compared to the authentic receptor.
• Tryptic maps of the 88,000 protein did not match authentic receptor subunits.
• The protein was resolved from authentic hormone-binding receptors and did not bind progesterone.
• Elution from affinity matrices was not progesterone-specific.

Conclusions:

• The 88,000 molecular weight protein is an artifact of steroid affinity resins, not the chick progesterone receptor.
• This protein does not possess progesterone-binding activity.