So once the heme A three and the copper B are in their fully reduced form, and a diatomic oxygen molecule is actually abstracted, and it is used to actually build a peroxide bridge between this structure and this structure here. Now, once we form this bridge, what happens next is, from the matrix of the mitochondria, two protons are abstracted, and those two protons are actually used to help break this bond. But before the two protons are used, two more of these reduced cytochrome C molecules are actually oxidized by protein complex four. So two of these cytochrome C's are actually oxidized. So they release two electrons. One of the electrons ends up on this copper.