At the end of this lecture, student will be able to

• Explain Co-enzymes


• The protein part of the enzyme, on its own, is not always adequate to bring about the catalytic activity.  Many enzymes require certain nonprotein factors, collectively referred to as coenzymes or cofactors

• Cofactors may be organic or inorganic in nature

• The non-protein, organic, Iow molecular weight and dialysable substance associated with enzyme function is known as coenzyme

• The functional enzyme is referred to as a holoenzyme which is made up of a protein part (apoenzyme) and a non-protein part (coenzyme)

• The term prosthetic group is used when a non-protein moiety is tightly bound to the enzyme which is not easily separable by dialysis

• The term activator is referred to the inorganic cofactor like Ca2+, Mg2+, Mn2+ etc. necessary to enhance enzyme activity

• Coenzymes undergo alterations during the enzymatic reactions, which are later regenerated

• Various types of Coenzymes are studied in detail under water-soluble vitamins

• Simply coenzymes are obtained from B-complex vitimines

Co-enzymes, Coenzymes

Non-vitamin coenzymes:

• Not all coenzymes are vitamin derivatives.  There are some other organic substances, which have no relation with vitamins but function as coenzymes, considered as non-vitamin coenzymes

Non-vitamin coenzymes,

Factors Affecting Co-enzyme Activity

pH and Temperature

The activity of co-enzymes is influenced by environmental factors such as pH and temperature. Optimal conditions ensure proper functioning of enzymes and their associated co-enzymes, while extremes can denature proteins and impair metabolic processes.

Concentration of Substrates

The availability of substrates affects the rate of enzymatic reactions involving co-enzymes. Adequate substrate concentrations promote efficient enzyme-substrate interactions, whereas deficiencies may lead to metabolic imbalances and dysfunction.

Disorders Related to Co-enzymes

Pellagra due to Niacin Deficiency

Pellagra is a condition caused by a deficiency of niacin, a precursor of NAD+. Symptoms include dermatitis, diarrhea, dementia, and death if left untreated, highlighting the essential role of niacin-derived co-enzymes in cellular metabolism.

Riboflavin Deficiency and its Effects

A deficiency in riboflavin, the precursor of FAD and FMN, can lead to various health issues, including skin disorders, eye abnormalities, and impaired energy metabolism. Riboflavin supplementation is essential for preventing these deficiencies and maintaining optimal health.


• The non-protein, organic, Iow molecular weight and dialysable substance associated with enzyme function is known as coenzyme


  1. What are co-enzymes, and how do they differ from enzymes? Co-enzymes are organic molecules that assist enzymes in catalyzing biochemical reactions. Unlike enzymes, which are proteins, co-enzymes are small molecules that bind loosely to the enzyme’s active site, aiding in the conversion of substrates into products.
  2. Why are co-enzymes essential for metabolism? Co-enzymes play crucial roles in metabolism by facilitating and regulating enzymatic reactions involved in the breakdown of nutrients, synthesis of macromolecules, and energy production. They serve as cofactors for numerous enzymes, enabling efficient metabolic processes.
  3. How do co-enzymes participate in redox reactions? Co-enzymes such as NAD+ and FAD serve as electron carriers in redox reactions. They accept electrons from substrates, becoming reduced, and then donate these electrons to other molecules, becoming oxidized. This transfer of electrons is essential for energy production and cellular respiration.
  4. What are some dietary sources of co-enzymes? Co-enzymes are derived from various dietary sources, primarily vitamins. For example, niacin (vitamin B3) is a precursor of NAD+ and NADP+, riboflavin (vitamin B2) is a precursor of FAD and FMN, and pantothenic acid (vitamin B5) is a precursor of Coenzyme A (CoA).
  5. What happens if there is a deficiency of co-enzymes in the body? Deficiency of co-enzymes can lead to metabolic imbalances and various health issues. For example, niacin deficiency can cause pellagra, characterized by symptoms like dermatitis, diarrhea, and dementia. Riboflavin deficiency can result in skin disorders, eye abnormalities, and impaired energy metabolism. Ensuring adequate intake of vitamins and nutrients is crucial for preventing co-enzyme deficiencies and maintaining optimal health.

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