Quaternary structure regulates hemin dissociation from human hemoglobin

Area of Science:

• Biochemistry
• Molecular Biology
• Protein Chemistry

Background:

• Hemoglobin's prosthetic heme group is crucial for oxygen transport.
• Understanding heme binding and release is vital for hemoglobin function and stability.

Purpose of the Study:

• To quantify hemin dissociation rates from human hemoglobin subunits.
• To investigate the influence of protein concentration and subunit assembly on heme release.

Main Methods:

• Hemin dissociation rate measurements using H64Y/V68F apomyoglobin as a hemin acceptor.
• Experiments conducted at pH 7.0 and 37°C.
• Comparison of native and recombinant human hemoglobins, including isolated chains and tetramers.

Main Results:

• Hemin dissociation from beta subunits is concentration-dependent, increasing significantly upon dimer formation.
• Hemin dissociation from alpha subunits is slower and less dependent on concentration.
• Monomeric chains exhibit much faster hemin dissociation rates than assembled subunits.
• Tetramer formation, particularly the alpha1beta2 interface, stabilizes heme binding.

Conclusions:

• Human hemoglobin structure modulates heme dissociation rates.
• The observed heme release kinetics suggest an evolutionary adaptation for efficient heme clearance post-red cell lysis.
• This rapid heme loss facilitates removal by serum proteins like albumin and apohemopexin.