This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Glycogen Metabolism and Glycogen Storage, Subject name: Biochemistry
Which of the following enzyme is absent in muscle? 
Select and explain. 
A. Glucose-1-phosphatase, B. Glucose 6 phosphatase, C. Glycogen phosphorylase, D. Thiophorase
B: Glucose 6 phosphatase
Answer: B: Glucose 6 phosphatase 
Explanation: Ref: Harper's Illustrated Biochemistry, 27th edition and Lippincott !s Biochemistry, 3rd editionExplanation:FATE OF MUSCLE GLYCOGENIn muscle, enzyme Glucose - 6- phosphatase is absent.This enzyme catalyzes the final step of glycogenolysis.Hence muscle glycogenolysis does not contribute to blood glucose directly.Glycogen of muscle can only be converted upto glucose - 6 - phosphate as muscle lacks glucose - 6 - phosphatase.Glucose - 6 - phosphate cannot cross the plasma membrane and enters the glycolytic cycle, where it is converted into lactic acid.This lactic acid cross the plasma membrane and reaches liver to form glucose