ABSTRACT
Overview Reducing power is available in a cell both as NADH and NADPH but these have quite distinct roles. NADH is oxidized by the respiratory chain to generate ATP via oxidative phosphorylation (Section L2). NADPH is used for biosynthetic reactions that require reducing power. Despite their similar structures (Section D1), NADH and NADPH are not metabolically interchangeable and so the cell must carry out a set of reactions that specifically create NADPH. This set of reactions is the pentose phosphate pathway (also known as the hexose monophosphate shunt or the phosphogluconate pathway). It takes place in the cytosol and is particularly important in tissues such as adipose tissue,
mammary gland and the adrenal cortex that synthesize fatty acids and steroids from acetyl CoA (Section K3). The activity of the pathway is very low in skeletal muscle, for example, which does not synthesize fatty acids or steroids.
