The following enzyme is required for the hexose monophosphate shunt pathway:

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