So this is a two step process that it catalyzes. So the substrate molecule of this particular enzyme is the arachidonic acid. And the arachidonic acid exists in its deprotonated state. What it does, this arachidonic acid basically is found within the hydrophobic region of the membrane. It moves into the active side of this enzyme, and it moves into the active side without actually having to interact with the aqueous environment of the Er lumen. Why?