Which statements about the binding of oxygen to heme are true?
1. The iron ion bound to the porphyrin group is +3.
2. In deoxyhemoglobin, the porphyrin nitrogens make up four of its six ligands, the nitrogen of His F8 makes up the fifth ligand, and the last remaining coordination site is empty.
3. When O2 is bound to the iron cation, His E7 makes a key H-bonding interaction with this ligand.
4. Heme is capable of binding other ligands, such as CO and NO, but it is the key interactions of oxygen with protein side chain residues that enhance the specificity for oxygen.
O2 and 3
3 and 4
2, 3, and 4
All statements are true.
