This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cofactor and prosthetic groups, Subject name: Biochemistry
Cofactor for xanthine oxidase: 
Select and explain. 
A. Zinc, B. Copper, C. Molybdenum, D. Selenium
C: Molybdenum
Answer: C: Molybdenum 
Explanation: Cu - required for all Oxidases e.g. Cytochrome c Oxidase Tyrosinase Ascorbic acid Oxidase Amino acid Oxidase Lysyl Oxidase and also for Cytoplasmic SOD (Super Oxide Dismutase) Two oxidases do not require Cu, instead, they require Molybdenum. These are: Xanthine Oxidase Sulfite Oxidase All Kinases need Mg2+(BUT Pyruvate Kinase need K+>> Mg2+) All Carboxylases and synthetases also need Mg2+ Cytoplasmic SOD requires copper WHEREAS Mitochondrial SOD requires Manganese(Mn)