Coenzymes, Cofactors and Prosthetic groups

• Cofactors


  Non-protein substances (i.e. not made from amino acids) that enzymes require in order to function properly
• Cofactors


  • Can be a temporary part of the enzyme or a permanent part (known as a prosthetic group)
• Coenzymes


  Organic non-protein cofactors that contribute to enzyme-catalysed reactions by accepting or donating hydrogen ions or chemical groups (e.g. phosphate groups)
• Prosthetic groups


  Cofactors that are a permanent part of the structure of the enzyme they assist, helping to form the final 3D shape of the enzyme
• Prosthetic group


  • Zinc ion acts as the prosthetic group for carbonic anhydrase (an enzyme found in red blood cells that converts CO2 and H2O into carbonic acid, H2CO3)
• Some enzymes can only function properly if another non-protein substance is present
• Inorganic ions may help to stabilise the structure of the enzyme or may actually take part in the reaction at the active site
• Inorganic cofactor


  • Chloride ions act as a cofactor for amylase
• In order for amylase to be able to digest starch into maltose, chloride ions must be present
• Inorganic ions that an enzyme requires in order to function are known as inorganic cofactors
• Some coenzymes are permanently bound to the enzyme they assist, often in or near the active site
• Some coenzymes only bind temporarily during the reaction
• Coenzymes link different enzyme-catalysed reactions into a sequence during metabolic processes, such as photosynthesis and respiration
• Vitamins are an important source of coenzymes
• Vitamins used to produce important coenzymes

  • Pantothenic acid (coenzyme A)
  • Nicotinic acid (NAD and NADP)
  • Vitamin B2 (riboflavin, FAD)
• During many of the reactions in respiration, the coenzymes NAD and FAD are alternately reduced and oxidised, transferring energy in the form of hydrogen ions
• The coenzyme NADP fulfils this same role in chloroplasts during photosynthesis
• The coenzymes ATP and coenzyme A act by transferring chemical groups, such as phosphate groups and acetyl groups (-CH3CO)
• Coenzymes are a type of cofactor that interact with enzymes