Now, once we form the oxalo acetate, the problem with the oxyloacetate is it can simply pass across the inner membrane of the mitochondria. We have to transform the oxalo acetate first into aspartate before it can actually move across this special antiporter protein system. And so the process by which we transform the oxyloacetate into aspartate is known as transamination. We essentially take an amino group from another molecule, namely the glutamate. We place it onto oxyloacetate, and that's how we form the aspartate. So in step four, shown here, the oxyloacetate cannot move across the inner mitochondrial membrane.