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
Iron is present in all of the following except 
Select and explain. 
A. Myoglobin, B. Cytochrome, C. Catalase, D. Pyruvate Kinase
D: Pyruvate Kinase
Answer: D: Pyruvate Kinase 
Explanation: None