https://www.ncbi.nlm.nih.gov/Structure/pdb/1QSH
PROTEIN (HEMOGLOBIN ALPHA CHAIN)PROTEIN (HEMOGLOBIN BETA CHAIN)PROTOPORPHYRIN IX CONTAINING FEPROTOPORPHYRIN IX CONTAINING MG
zinc protoporphyrinmagnesiumiiixstabilize
https://www.rcsb.org/structure/1QSI
MAGNESIUM(II)-AND ZINC(II)-PROTOPORPHYRIN IX'S STABILIZE THE LOWEST OXYGEN AFFINITY STATE OF HUMAN HEMOGLOBIN EVEN MORE STRONGLY THAN DEOXYHEME
rcsb pdbzinc protoporphyrinmagnesiumiiix