And let's begin with Argininosuxenase deficiency. So Arginosuxinase is the enzyme that essentially catalyzes step four, the conversion of Arginosuxanate to Arginine and also forming the fumarate. Now, normally what this does is this reaction continually replenishes the Arginine, which essentially keeps reaction five, which keeps reaction five going. And so by keeping this reaction going, we produce the ornathine that we need for step number two. And we also produce the urea, which is ultimately excreted by our kidney. Now, if this reaction stops, so let's stop this reaction.