A protein with multiple heme-binding sites from rabbit serum.

Area of Science:

• Biochemistry
• Proteomics

Background:

• Hemin and protoporphyrin IX are crucial molecules in biological systems.
• The identification and characterization of heme-binding proteins are essential for understanding various physiological and pathological processes.

Purpose of the Study:

• To isolate and characterize a novel heme-binding protein from rabbit serum.
• To investigate the binding affinity, capacity, and mechanism of the isolated protein for heme and protoporphyrin IX.

Main Methods:

• Affinity chromatography using hemin-conjugated agarose for protein isolation.
• Spectrophotometric titration and sedimentation velocity analysis for binding studies.
• Amino acid composition analysis to determine protein characteristics.

Main Results:

• A 93,000 molecular weight protein (HBP.93) with high affinity for hemin and protoporphyrin IX was isolated.
• HBP.93 exhibits a unique amino acid composition with high proline and histidine content.
• The protein demonstrates a high capacity for heme binding (25-35 mol hemin/mol protein) with dissociation constants in the 10(-7) to 10(-6) M range.
• Spectroscopic and sedimentation data suggest a bisimidazol-type coordination of heme iron and altered protein mobility upon heme binding.

Conclusions:

• HBP.93 is a novel, high-capacity heme-binding protein from rabbit serum.
• The binding mechanism likely involves bisimidazol-type coordination of heme iron.
• The high histidine content and heme-binding properties suggest a potential relationship with human alpha 2-histidine-rich glycoprotein.