This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Structure and function of protein, Subject name: Biochemistry
Heme is which porphyrin? 
Select and explain. 
A. Type I, B. Type II, C. Type III, D. Type IV
C: Type III
Answer: C: Type III 
Explanation: The protoporphyrinogen-III is oxidized by the enzyme protoporphyrinogen oxidase to protoporphyrin-III in the mitochondria. The xidation requires oxygen.The methylene bridges (-CH2) are oxidized to methenyl bridges ( -CH=) and colored porphyrins are formed.Protoporphyrins -9 is thus formed. The last step in the formation of heme is the attachment of ferrous iron to the protoporphyrin. The enzyme is heme synthase or ferrochelatase, which is also located in the mitochondria. REFERENCE : DM VASUDEVAN TEXTBOOK SEVENTH EDITION ; PAGE NO : 273.