And that means Myoglobin can only bind onto one oxygen, while Hemoglobin can bind four different oxygen atoms, as we'll see in just a moment. So on the bottom of that fe, we have the bond form between the nitrogen of this histogine residue and this metal atom found in that heme group. Now, in this particular state, the electron density around that fe is simply too large for that fe to actually fit inside the center of that plane. And that's exactly why this fe atom will be found slightly below the protoporphine plane, as shown in the following diagram. So in deoxy hemoglobin or deoxy myoglobin. When the protein is not bound to the oxygen, the iron atom remains unbound to oxygen.