Many of the substances we call vitamins, are in fact coenzymes or are converted metabolically to coenzymes. The so-called B vitamins are typical of this group of compounds. The terms niacin and Vitamin B3 have both been used to refer to both nicotinamide and nicotinic acid:
Niacin, which is essential in the diets of mammals, is incorporated into NAD and NADH. These two substances form a redox couple that can transfer a hydride as sodium borohydride does, or accept one like the Jones reagent.
| NAD in a Jmol Window |
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| Riboflavin |
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| FAD |
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| Riboflavin (Jmol) | FAD (Jmol) |
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FAD accepts net two protons and two electrons (that is, a molecule of hydrogen) to produce FADH. It can do this either as NAD does, accepting hydride (two electrons), or as shown below in two one-electron steps. This coupling of two- and one- electron processes through FAD/FADH is important in cellular respiration.
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