The following enzyme is required for the hexose monophosphate shunt pathway:: (A) Glucose-6-phosphatase, (B) Phosphorylase, (C) Aldolase, (D) Glucose-6-phosphate dehydrogenase
Answer is D. 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