Sources of Coenzymes

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The human body survives and thrives through the actions of proteins called enzymes, which catalyze reactions necessary for life to exist. Most of these enzymes, however, need a helping hand to get the job done, and that is where coenzymes come into play. Our bodies do not produce most of these critical components; fortunately, we receive plenty of the biological precursors to coenzymes in our diet.

What Are Coenzymes?

  • Most enzymes in the body require the assistance of one or more cofactors, which can be as simple as a metal ion. However, many cofactors are organic molecules called coenzymes. The protein chain of the enzyme is catalytically inactive without the addition of coenzymes or metal ion cofactors.

Example Function

  • A good example of coenzyme function is the action of nicotinamide adenine diphosphate (NAD+) in oxidation-reduction reactions. Anytime you drink alcoholic beverages, an enzyme in your liver oxidizes the ethanol in your blood into an aldehyde. This enzyme, alcohol dehydrogenase, needs a molecule which can receive the electrons from ethanol. The positively-charged NAD+ can easily accept the electrons (and the proton that follows them) to form NADH. Thus, the presence of NAD+ allows alcohol dehydrogenase to catalyze aldehyde production.

Coenzyme Sources

  • Most of the coenzymes in our body are produced through the conversion of dietary vitamins. For example, the vitamin niacin is the biological precursor to NAD+. Folic acid, another dietary necessity, is converted to tetrahydrofolate (THF), which is a coenzyme for carbon-transfer reactions. Dietary biotin is converted into biocytin, which assists carboxylation reactions. B vitamins are the most important coenzyme precursors; these are converted into a myriad of coenzymes such as thiamine pyrophosphate and flavin coenzymes.

B Vitamin Sources

  • The only B vitamins stored long-term by the body are B5 (pantothenic acid) and B12 (cyanocobalamin); thus, a daily supply of B vitamins is important for overall health and bodily function. A good diet of meat, poultry and fish will effectively supply the body with enough B vitamins, but these nutrients can also be found in smaller amounts in legumes and some vegetables. Vegetarians either need to eat plenty of beans or include a vitamin supplement in their diet.

Folic Acid, Niacin and Biotin Sources

  • Folic acid is stored in the liver, and can be found in orange juice, green vegetables, eggs, veal and whole grains. Niacin, the precursor to nicotinamide coenzymes, is water-soluble and must be replenished every day. This vitamin can be found in poultry, meat and fish, but fortunately for vegetarians, our bodies can convert tryptophan into the required coenzymes. This amino acid can be found in rice, legumes and seeds. Biotin is stored in the brain, liver and kidneys in very small amounts and can be found in liver, egg yolk and nuts. We usually don't need any dietary biotin because bacteria in our colon produce the nutrient for us.

References

  • Human Anatomy and Physiology, Sixth Edition; Elaine N. Marieb; 2004
  • Biochemistry, Third Edition; Voet and Voet; 2004
  • Photo Credit Image by Flickr.com, courtesy of thebittenword.com
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