At the center of each one of these C subunits is an aspartate residue that can readily bind protons under acidic conditions. So now that we know what the structure of what the structure of the f one region is, we can actually deduce what the mechanism of proton movement looks like. So let's take a look at the following three steps. And these are the diagrams that correspond to each one of these steps. So let's begin with diagram number one. So again we have the inner mitochondrial membrane.