Ketohexokinase (fructokinase, KHK) catalyzes the phosphorylation of fructose to fructose-1-phosphate (F1P), the first step in the metabolism of dietary fructose. KHK can also phosphorylate several other furanose sugars. It is found in higher eukaryotes where it is believed to function as a dimer and requires K(+) and ATP to be active. In humans, hepatic KHK deficiency causes fructosuria, a benign inborn error of metabolism.