What is the significance of the hexacoordinate heme in some hemoglobin variants?

A Increased affinity for oxygen
B Decreased affinity for oxygen
C Stabilization of the heme group against oxidation ✓
D Facilitation of the binding of carbon monoxide

Explanation

The hexacoordinate heme is characterized by the presence of two axial ligands, which can stabilize the heme group against oxidation and increase its resistance to degradation.

Source

Biochemistry journal articles
Hematology Hematology: Hemoglobin and Oxygen Transport Hematology: Hemoglobin and Oxygen Transport Hard MEDICAL Confidence: medium