This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of carbohydrate, Subject name: Biochemistry
Fluoride, used in the collection of blood samples for glucose estimation, inhibits the enzyme 
Select and explain. 
A. Glucokinase, B. Hexokinase, C. Enolase, D. Glucose-6-phosphatase
C: Enolase
Answer: C: Enolase 
Explanation: Enolase requires Mg+ +, and by removing magnesium ions, fluoride will irreversibly inhibit this enzyme. Thus, fluoride will stop the whole glycolysis. So when blood collecting for sugar estimation, fluoride is added to the blood. If not, glucose is metabolized by the blood cells, so that lower blood sugar values are obtained.Ref: DM Vasudevan, 7th edition, page no: 111