So what happens in step four? So ultimately, the second amino group that came from aspartate ends up on the arginine when this reaction happens, but the carbon skeleton that was found on the aspartate essentially ends up on the fumerate. In fact, the carbon skeleton of the aspartate is fumerate. Now, fumerate is important because fumerate is the link. It's the bridge between the urea cycle and gluconeogenesis, the production of glucose. So remember, in the liver we have gluconeogenesis and in gluconeogenesis we can ultimately form malate from fumerate.