Familial fructokinase deficiency causes no symptoms because:: (A) Hexokinase can phosphorylate fructose, (B) Liver aldolase can metabolize it, (C) Excess fructose does not escape into the urine, (D) Excess fructose is excreted through feces
Answer is A. Fructose metabolism Fructokinase is the first enzyme for fructose metabolism. It conves fructose to fructose-1-P. In Fructokinase deficiency, Hexokinase (a non specific enzyme) can phosphorylate fructose as well as other sugars but it has high km (low affinity) for fructose. Glucose is the true substrate for this enzyme. Fructose 6-phosphate - the end product of Hexokinase reaction can enter glycolytic pathway to be utilized fuher, so it does not accumulate to produce toxic effects. EXTRA EDGE- Fructokinase deficiency causes Essential Fructosuria, while Aldolase B deficiency causes Hereditary Fructose Intolerance