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
True about isoenzymes is/are: 
Select and explain. 
A. Different km value, B. Act on different substrate, C. Same electrophoretic mobility, D. All
A: Different km value
Answer: A: Different km value 
Explanation: Isozymes are the physically distinct forms of the same enzymes that catalyze the same reaction, and differ from each other structurally, electrophoretically and immunologically. They differ in their physical propeies because of genetically determined difference in amino acid sequence. They are separated by electrophoresis as they have different electrophoretic mobility. They have different Km value. Isoenzyme of an oligomeric enzyme process differ in combination of its peptide protomer.