This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Enzyme Kinetics, Subject name: Biochemistry
Km of an enzyme is: 
Select and explain. 
A. Dissociation constant, B. The normal physiological substrate concentration, C. The substrate concentration that produces half maximum velocity, D. Numerically identical for all isozymes that catalyze a given reaction
C: The substrate concentration that produces half maximum velocity
Answer: C: The substrate concentration that produces half maximum velocity 
Explanation: Ans. C. The substrate concentration that produces half maximum velocityThe substrate concentration that produces half maximal velocity (v termed the K value or Michaelis constant)