• There are substances?other than?substrates and inhibitors that?interact?with?enzymes
  • Some enzymes can only?function properly?if another?non-protein substance?is present
  • For example, some enzymes are?inactive?until they combine with a non-protein substance that?changes?their?tertiary structure?(allowing the?active site?to?bind?correctly with the?substrate)

   

• These substances are broadly known as?cofactors

Cofactors

• Some enzymes require?inorganic ions?to function properly
• Particular inorganic ions may help to?stabilise?the?structure?of the enzyme or may actually?take part in the reaction?at the?active site
  • For example,?chloride ions?act as a cofactor for?amylase
  • This means that in order for amylase to be able to digest starch into maltose, chloride ions must be present

   

• The inorganic ions that an enzyme requires in order to function are known as?inorganic cofactors

Coenzymes

• Larger?organic?(carbon-containing)?cofactors?are known as?coenzymes
  • 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. For example, many vitamins in the B vitamin group are used in the production of important coenzymes, including:
  • Pantothenic acid, a key component of?coenzyme A?(a coenzyme required for the oxidation of pyruvate during the link reaction that occurs between the glycolysis and Krebs cycle stages of respiration)
  • Nicotinic acid, used to produce the coenzymes?NAD?and?NADP?(coenzymes required in many different metabolic reactions, including many of the reactions that take place during photosynthesis and respiration)
  • Vitamin B??(riboflavin), used to produce the coenzyme?FAD?(a coenzyme required in the Krebs cycle during respiration)

   

Examples of coenzyme functions

• 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 in a different way, by?transferring chemical groups. For example:
  • ATP is responsible for the transfer of?phosphate groups?between respiration and energy-consuming processes in cells
  • Coenzyme A is responsible for the transfer of an?acetyl group?(-CH?CO) from fatty acids and glucose during respiration

   

Coenzymes are a type of cofactor that interact with enzymes and allow them to function properly

Prosthetic groups

• Some cofactors are actually a?permanent part?of the structure of the enzyme they assist
  • These cofactors are known as?prosthetic groups

   

• Prosthetic groups are essential to the enzyme?functioning properly, as they help to form the final?3D shape?of the enzyme
  • For example, by forming part of the?active site?of the enzyme, a?zinc ion?acts as the prosthetic group for?carbonic anhydrase?(an enzyme found in red blood cells that converts CO? and H?O into carbonic acid, H?CO?)

   

Summary

• Cofactors?are?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?are?organic?non-protein cofactors. Coenzymes contribute to enzyme-catalysed reactions by?accepting?or?donating?hydrogen ions?or?chemical groups?(e.g. phosphate groups)