So these groups on the hemoglobin molecule can actually bind H plus ions. And by binding H plus ions, those ions can then participate in forming stabilizing salt bridges. And to see what we mean by that, let's take a look at the following diagram. So this is the histidine 141 residue found on the beta one subunit. And this is a nearby residue on the same beta one subunit, the aspartate 94. Now, notice in this particular case, so at a relatively high PH of, let's say, 7.4, which is the PH inside our lungs, this nitrogen.