And so now what we want to use is we want to basically transform or remove the carbon skeleton that came from Aspartate. So we want to keep this nitrogen group shown here on this structure. But we want to remove this carbon skeleton and recycle that carbon skeleton. And so that's what happens in step four. The enzyme argininosuxinase basically catalyzes the removal of this carbon skeleton to form fumarate. And we also form arginine as shown here.