Cofactors and Chemistry

Nicotinamide Adenine Dinucleotide

Chemical structures of NAD+ and NADH
The part that is directly involved in the redox chemistry is circled in magenta		3D representation NAD+ (P=orange N=blue C=gray)

Vitamin B3 Dependence: Humans do not synthesize Nicotinamide (the active portion of NAD+ and circled in magenta above) and therefore require its intake as part of the diet. Nicotinamide is one of the (many) B types typically called vitamin B3. You may read much more about this and issues regarding its synthesis and deficiencies here.

There are two version of this cosubstrate, NAD+ and NADP+. They differ in structure solely in that NADP+ has an additional phosphate bonded to the sugar (on the right in the top structure above).

NAD and NADP have virtually the same role in terms of their chemistry. They are a cosubstrate in redox reactions (not tightly bound to the enzyme but freely diffusible) in which a hydride is transferred to or from the other substrate. They can only transfer two electrons at a time in the form of a hydride (H-)

NAD and NADP have slightly different roles physiologically. typically NADP is associated with reactions that are generally thought as building molecules, while NAD is involved in reactions that are typically thought as tearing down molecules.

SOME ENZYMES USING THIS COFACTOR

lactate dehydrogenase (enzyme in muscle cells - most important during strenuous exercise) - more about this enzme in module 6
pyruvate dehydrogenase (key transition enzyme between glycolysis and the Krebs cycle) - more about this enzme in module 6
glyceraldehyde-3-phosphate dehydrogenase (enzyme of the glycolysis pathway ) - more about this enzme in module 6