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
Which enzyme catalyses substrate level phosphorylation in Kreb's cycle? 
Select and explain. 
A. ∝ Ketoglutarate dehydrogenase, B. Succinate thiokinase, C. Succinate dehydrogenase, D. Isocitrate dehydrogenase
B: Succinate thiokinase
Answer: B: Succinate thiokinase 
Explanation: Succinate thiokinase catalyses substrate level phosphorylation of TCA cycle. It is the only enzyme of TCA cycle doing that.