Co Factor 8o4w

Cofactor • Many enzymes require the presence of a nonprotein substance called a cofactor. • Cofactors may be organic or inorganic. • There are three types of cofactors. • the inactive protein molecule is known as an apoenzyme. • an active enzyme, it is called a holoenzyme.

Type of cofactor • Prosthetic groups • Coenzymes • Enzyme activators

Coenzymes • small, non-protein organic molecules. • they bind loosely and temporarily to the active site of the enzyme. • play an accessory role in enzyme-catalyzed processes, • acting as a donor or acceptor of a substance involved in the reaction. • When combined with an inactive apoenzyme, coenzymes form a complete, active enzyme called the holoenzyme

• The coenzymes readily detach and help to transfer chemical group, atoms or electrons from one enzyme to another

• Many coenzymes are derivatives of vitamins especially group B vitamins. NAD (nicotinamide adenine dinucleotide) for example is formed from niacin. • It is a coenzyme for a number of dehydrogenase enzymes and acts as a hydrogen acceptor.

Prosthetic group • is a non-protein organic molecule • tightly (often covalently) bound to a particular enzyme molecule. • involved in the catalytic function of the enzyme. • Haem is an example of a prosthetic group found in cytochromes and haemoglobin, which carries electrons and/or oxygen.

Ion activator • Activators are inorganic ions such as Ca 2+ Zn 2+ , Mg 2+, Fe 2+ and CF. • They may attach temporarily to the enzyme and change its active site t • make the shape more suitable for a reaction to take place. • The ion may also bind the enzyme and substrate together.

• Help draw electron away from the substrate molecule-making bond less stable-eisier to break • Example-refer your book

• Calcium ions are needed to activate thrombokinase which converts prothrombin to thrombin in blood clotting. • Chloride ions increase salivary amylase activity.

• The largest number of vitamins (e.g., B complex vitamins) function as precursors for enzyme cofactors, that help enzymes in their work as catalysts in metabolism. • In this role, vitamins may be tightly bound to enzymes as part of prosthetic groups: • For example, biotin is part of enzymes involved in making fatty acids. • Vitamins may also be less tightly bound to enzyme catalysts as coenzymes, detachable molecules that function to carry chemical groups or electrons between molecules. • For example, folic acid carries various forms of carbon group – methyl, formyl, and methylene – in the cell. • Although these roles in assisting enzyme-substrate reactions are vitamins' best-known function, the other vitamin functions are equally important.