This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of lipid, Subject name: Biochemistry
The only energy-requiring step in fatty acid oxidation is catalyzed by ______ enzyme? 
Select and explain. 
A. Thiokinase, B. Acyl co A dehydrogenase, C. Thiolase, D. Beta hydroxy Acyl co A dehydrogenase
A: Thiokinase
Answer: A: Thiokinase 
Explanation: In the presence of ATP and coenzyme A, the enzyme acyl-CoA synthetase (thiokinase) catalyzes the conversion of a fatty acid to acyl-CoA. Reference: Harper's Illustrated Biochemistry 30th Edition Pg 224