Magnetic mechanism for the biological functioning of hemoglobin

TL;DR

This study combines advanced computational methods with experimental data to demonstrate that magnetic interactions, specifically antiferromagnetic correlations in the heme group, are fundamental to hemoglobin's biological function.

Contribution

It provides the first detailed theoretical and experimental evidence linking magnetism to hemoglobin's function, highlighting the role of antiferromagnetic correlations in its activity.

Findings

Magnetic moments develop in the porphyrin layer with antiferromagnetic coupling to Fe.

The calculations match experimental magnetic susceptibility data.

Antiferromagnetic correlations explain hemoglobin's properties like the Bohr effect.

Abstract

The role of magnetism in the biological functioning of hemoglobin has been debated since its discovery by Pauling and Coryell in 1936. The hemoglobin molecule contains four heme groups each having a porphyrin layer with a Fe ion at the center. Here, we present combined density-functional theory and quantum Monte Carlo calculations for an effective model of Fe in a heme cluster. In comparison with these calculations, we analyze the experimental data on human adult hemoglobin (HbA) from the magnetic susceptibility, Mossbauer and magnetic circular dichroism (MCD) measurements. In both the deoxygenated (deoxy) and the oxygenated (oxy) cases, we show that local magnetic moments develop in the porphyrin layer with antiferromagnetic coupling to the Fe moment. Our calculations reproduce the magnetic susceptibility measurements on deoxy and oxy-HbA. For deoxy-HbA, we show that the anomalous MCD signal in the UV region is an experimental evidence for the presence of antiferromagnetic Fe-porphyrin correlations. The various important properties of hemoglobin are explained based on the antiferromagnetic correlations including the Bohr effect and cooperativity. This analysis shows that magnetism is involved in a fundamental way in the functioning of hemoglobin.