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
The following enzyme is required for the hexose monophosphate shunt pathway: 
Select and explain. 
A. Glucose-6-phosphatase, B. Phosphorylase, C. Aldolase, D. Glucose-6-phosphate dehydrogenase
D: Glucose-6-phosphate dehydrogenase
Answer: D: Glucose-6-phosphate dehydrogenase 
Explanation: Glucose-6-phosphate is oxidized by NADP+ dependent Glucose-6-phosphate dehydrogenase (GPD). 6-phospho glucono lactone is formed.
One molecule of NADPH is formed in the reaction. This is the rate-limiting step. Regulation is effected by this enzyme
 
Reference: Vasudevan 7th  ed, pg 130