In muscle tissue, obviously glucose is used through glycolysis to make peruvate produce ATP. The thing is that muscle uses a lot of proteins and it doesn't just use the protein and keep using it for your whole life. When you use a protein, it tends to break down and have a byproduct - ammonia. Ammonia can be toxic when it... Excess. Excess. So we need a way of getting rid of that ammonia, but you can't just throw it straight from the muscle into the bloodstream. Here in the liver, the alanine will turn back into pyruvate, but will have to steal some alpha-ketoglutarate