Nonprotein components of certain enzymes are called cofactors. If the cofactor is organic, then it is called a coenzyme. Coenzymes are relatively small molecules compared to the protein part of the enzyme and many of the coenzymes are derived from vitamins. The coenzymes make up a part of the active site, since without the coenzyme, the enzyme will not function.
- Flavin Adenine Dinucleotide (FAD)
- The structure shown on the left is for FAD and is similar to NAD+ in that it contains a vitamin-riboflavin, adenine, ribose, and phosphates. As shown it is the diphosphate, but is also used as the monophosphate (FMN).
- Nicotinamide Adenine Dinucleotide (NAD)
- Nicotinamide is from the niacin vitamin. The NAD+ coenzyme is involved with many types of oxidation reactions where alcohols are converted to ketones or aldehydes. It is also involved in the first enzyme complex 1 of the electron transport chain.
- Vitamin A: β-Carotene
- β-carotene is the molecule that gives carrots, sweet potatoes, squash, and other yellow or orange vegetables their orange color. It is part of a family of chemicals called the carotenoids, which are found in many fruit and vegetables, as well as some animal products such as egg yolks. Carotenoids were first isolated in the early 19th century, and have been synthesized for use as food colorings since the 1950s.
- Vitamin B₁₂: Cobalamin
- Cobalamin, or Vitamin B12, is the largest and the most complex out of all the types of Vitamins. The discovery of Cobalamin was made as scientists were seeking to find a cure for pernicious anemia, an anemic disease caused by an absence of intrinsic factor in the stomach.