Nitric oxide synthase takes the amino acid arginine and splits it into two products: nitric oxide, a signaling molecule that controls blood vessel tone, and citrulline, the leftover amino acid.
Well, the thing that arginine does that directly goes over to the vascular system is arginine can be acted on by an enzyme called nitric oxide synthase. And in biochemistry, whenever an enzyme's called synthase, it's a synthetic enzyme, meaning it makes something. So when you have that, you have a substrate like arginine, and then you have nitric oxide synthase, which is the enzyme, they come together and the way that the enzyme is formed, it knocks the NO, the nitric oxide off of the arginine. And then you wind up with a product and then a leftover. The product is nitric oxide and the leftover part is going to be called citrulline, which is another amino acid.
