Cofactors, Coenzymes, Prosthetic groups

Difference between cofactors and coenzymes

  • Enzymes sometimes need a non-protein ‘helper’ component for them to carry out their function as biological catalysts. → Known as ‘Cofactors’

  • ‘Coenzymes’ are if the Cofactor is an organic molecule

  • Cofactors ‘Non-protein helpers’ can : Help the substrate bind (by altering the active site to the right shape for the substrate to fit), Participate in reactions (by transferring electrons or atoms), Stabilize the enzyme (during a reaction).

  • Inorganic cofactors are obtained via diet as minerals - iron, calcium, chloride, zinc ions. Eg → amylase (enzyme for breakdown of starch) contains chloride ion necessary for the formation of a correctly shaped active site.

  • Coenzymes are derived from vitamins. Eg → Vitamin B5 is used to make Enzyme A - coenzyme responsible for the breakdown of fatty acids and carbs in respiration.

Prosthetic groups

  • Prosthetic groups are Cofactors - required by certain enzymes to carry out their function

  • They’re tightly bound and form a permanent feature of the enzyme structure. Eg → zinc ions form important part of structure of ‘carbonic anhydrase’, an enzyme necessary for metabolism of CO2.

Precursor activation

  • Many enzymes are produced in an inactive form known as ‘ inactive precursor enzymes ‘. Especially enzymes that could: cause damage within the cells producing them or to tissues where they are released, or enzymes whose actions needs to be controlled and only activated under certain conditions.

  • Precursor Enzymes need to change in structure (mostly active site) to be activated. This can be achieved by addition of a cofactor.

  • Before Cofactor is added, the precursor enzyme/protein is called an apoenzyme. When Cofactor is added, enzyme activated = ‘Holoenzyme’

  • Sometimes, change in tertiary structure can be due to:

    • Action of another enzyme

    • Change in conditions such as pH or Temperature - These enzymes are known as ‘Zymogens’ or ‘Proenzymes’.

  • When inactive pepsinogen is released into the stomach to digest proteins, acid pH brings about the transformation into the active enzyme pepsin. This adaptation protects the body tissues against self digestion.