This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
The enzyme common to both glycogenolysis and glycogenesis is: 
Select and explain. 
A. Glycogen phosphorylase, B. Glycogen synthase, C. Glucotransferase, D. Phosphoglucomutase
D: Phosphoglucomutase
Answer: D: Phosphoglucomutase 
Explanation: Ans. D PhosphoglucomutaseThe combined action of phosphorylase and these other enzymes leads to the complete breakdown of glycogen. The reaction catalyzed by phosphoglucomutase is reversible, so that glucose 6-phosphate can be formed from glucose I-phosphate. In liver (and kidney), but not in muscle, glucose 6-phosphatase hydrolyzes glucose 6-phosphate, yielding glucose that is expoed, leading to an increase in the blood glucose concentration. "