NADPH is a reductant, meaning it is a reducing agent that donates electrons to other molecules. It is often used as a cofactor in anabolic reactions (reactions that build complex molecules), like photosynthesis and fatty acid biosynthesis.
The key concept to understand is that NADPH itself is not consumed in the reaction, it is simply changed from its reduced form (NADPH) to its oxidized form (NADP+).
To answer your question more precisely, we can say that NADPH reacts with specific enzymes and their substrates. Here are some examples:
* Photosynthesis: NADPH reduces carbon dioxide to glucose in the Calvin cycle. In this case, NADPH reacts with the enzyme ferredoxin-NADP+ reductase and carbon dioxide as the substrate.
* Fatty acid biosynthesis: NADPH reduces acetyl-CoA to fatty acids. In this case, NADPH reacts with the enzyme fatty acid synthase and acetyl-CoA as the substrate.
So, while NADPH is not a reactant in a traditional sense, it plays a crucial role in many metabolic pathways by providing electrons for reduction reactions.
