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
Muscles cannot contribute to raising blood glucose by glycogenolysis due to lack of - 
Select and explain. 
A. Glucokinase, B. Phosphoglucomutase, C. G-6-phosphatase, D. Musclephosphorylae
C: G-6-phosphatase
Answer: C: G-6-phosphatase 
Explanation: Ans. is 'c' i.e., G-6-phosphatase o Glucose-6-phosphatase is absent in muscles therefore, glucose-6-phosphate cannot be degraded to free glucose in muscles.o Moreover, glucose-6-phosphate cannot diffuse out of the muscles.o Therefore, muscle cannot provide glucose to maintain blood glucose level.o Rather, muscle glycogen acts as a source of energy: the glucose-6-phosphate enters the glycolysis to produce energy.