Many enzymes require non-protein cofactors to help catalyze reactions. There are two types of enzymes: simple protein enzymes composed only of polypeptide chains, and conjugated enzymes containing both a protein and non-protein cofactor. The cofactor, combined with the protein apoenzyme, form the active holoenzyme. Cofactors can be inorganic ions or complex organic coenzymes, and can be tightly bound prosthetic groups or loosely attached coenzymes. Vitamins often act as precursors to coenzymes, helping enzymes function in catalytic reactions.

1. Enzyme Cofactors
Robin Singh
B.Sc (hons) Biochemistry

2. Many enzymes need non-protein parts called
cofactors that help in catalysis
Two Types of Enzymes
1. Simple Protein Enzymes = Composed of a
polypeptide chain (protein only
2. Conjugated Enzymes = Protein + Non-
proteinous part
----The non-proteinous part of a conjugated enzyme
is called a cofactor while the proteinous part of an
enzyme is referred to as apoenzyme……
Cofactor + apoenzyme = Holoenzyme

3. Only the combination of an apoenzyme with its
cofactor (i.e., a holoenzyme) is operative (a
holoenzyme also refers to the assembled form of a
multiple subunit protein).

4. • The cofactors can be inorganic ions or coenzymes
(complex organic or metallo-organic molecules).
• Some cofactors bind to the enzyme protein very tightly
(non-covalently or covalently), they are thus called
prosthetic groups, while loosely attached non-
proteineous components are called as Coenzymes
• Coenzymes usually function as transient carriers of
specific function groups. Coenzymes can act as Co-
Substrate….
• Vitamins (organic nutrients required in small amount
in the diet) have been found to often act as precursors
of coenzymes.

6.  Prosthetic group is present in enzymes and non-
enzyme proteins.
 Prosthetic group is always tightly attached to the
proteinous part of an enzyme,
 Prosthetic group mainly participate in Redox
reactions
 Example is heme, a prosthetic group present in
cytochrome oxidase….

7. Role of coenzyme and cofactor
The first type of enzyme partner is a group called cofactors, or
molecules that increase the rate of reaction or are required for
enzyme function. Cofactors are not proteins but rather help
proteins, such as enzymes, although they can also help non-
enzyme proteins as well. Examples of cofactors include metal ions
like iron and zinc.

8. Thank you