Enzyme cofactors

mudasir malik

1. Enzyme Cofactors

2. Many enzymes need non-protein parts called cofactors that help in catalysis Two Types of Enzymes Simple Protein Enzymes = Composed of a polypeptide chain (protein only 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.

5. 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….

6. Coenzymes are of two types Group transferring coenzymes….they are involved in transferring group from one substrate to another substrate Coenzyme-A is involved in the transfer of acyl group from one substrate to another substrate Biotin is involved is in transfer of –COO Pyridoxal phosphate is involved in transfer of amino group 2. Electron transferring coenzymes …they are involved in redox reactions NAD and NADH+H FAD and FADH2 Most of the coenzymes are Vitamin B derivatives Coenzymes can act as co-substrates

7. (Vitamins)

8. Some common coenzymes Acyl groups and others Coenzyme A Lipoic acid Thiamine pyrophosphate Pyridoxal phosphate 5 ’-Deoxyadenosyl-cobalamin Transfers Acyl groups Acyl groups Aldehydes Amino groups Alkyl groups

9. Thiamine (Thiamine pyrophosphate…..Vitamin B1) Catalyzes decarboxylation of keto acids, a feature of primary metabolism e.g. pyruvic acid → acetaldehyde in glycolysis pyruvic acid → acetyl-CoA usually found in phosphate form

10. Flavin Adenine mononeucleotide and Flavin adenine dinucleotide (Vitamin B2) Involved in redox rxns of C-C bonds Metabolism of carbs, fat, protein

11. Nicotinamide Adenine dinucleotide (Vitamin B3) As part of NAD + system, catalyzes redox rxns of alcohols/carbonyl compounds

12. Coenzyme A ( Panthothenic acid OR Vitamin B5) Synthesis of fatty acids (acetate pathway), some peptides, phenylpropanoids , isoprenoids Fat, carbs and protein metabolism

13. Pyridoxamine , pyridoxal phosphate & pyridoxine ( Vitamin B6 ) Catalyzes transaminations & decarboxylations of amino acids Metabolism  energy pyridoxine

14. Tetrahydrofolate (Vitamin B9) Role: Tetrahydrofolate functions in one-C metabolism as a carrier of methyl, methylene or formyl groups Involved in amino acid and nucleotide metabolism, red blood cell formation

15. Metal ions perform three distinct functions during enzyme catalysis Mediating Oxidation-reduction reactions through reversible changes in the metal ion oxidation state Binds to substrate and properly orient them for reactions Electrostatically stabilizes or shield negative charges ------------ ---1/3 of all known enzymes require metal ions for their catalytic activities Metalloenzymes …metal ion is tightly bound to the enzyme Metal activated enzymes ….metal ion is loosely attached to the enzyme Two types of Enzymes on the basis of metal ions