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
All of the following enzymes are regulated by calcium or calmodulin, except: 
Select and explain. 
A. Adenylate cyclase, B. Glycogen synthase, C. Guanylyl cyclase, D. Hexokinase
D: Hexokinase
Answer: D: Hexokinase 
Explanation: Adenyl cyclase, guanylate cyclase and glycogen synthase enzymes (but not hexokinase) are activated by calcium and calmodulin.