It cycles between glucose and Alanine, but it's also returned back to its source, the skeleton muscle cell. But the ammonium is transported into the skeletal, into the liver. It's not returned back to the skeleton muscle. Now, so the glucose Alanine cycle is one pathway by which we can transport the ammonium from our target tissue, our skeletal muscle tissue, to our liver. But there is another method and that utilizes an enzyme known as glutamine synthetase. So glutamine synthetase is an ATP driven enzyme.