COENZYMES
- Coenzyme derived from water-soluble vitamins.
- Coenzymes function as either –
A) Co- substrates- In a group transfer reaction coenzyme acts either a donar or acceptor. for eg, pyridoxal phosphate (a co-substrate in transmination reaction), Most common mechanism of coenzymes.
B) Prosthetic groups- coenzyme covalently bound to the enzyme.For example, biotin is the prosthetic group for carboxylases.
Classification of Coenzyme–
a) For transfer groups other than hydrogen-
| Vitamin | Coenzyme |
Function as Coenyme
|
Entity transferred | ||
| Riboflavin (Vit B2) | FAD, FMN | Oxidation & reduction reaction | Hydrogen atoms | ||
| Niacin | NAD+, NADH+ | Oxidation & reduction rxn | Hydride ion | ||
| Pyridoxin (Vit B6) | Pyridoxial phosphate (PLP) | Decarboxylation of amino acids | Amino group | ||
| Folic acid | Tetrahydrofolate | Carrier of one carbon group | One carbon group | ||
| Pentothenic acid | Coenzyme A | Acyl carrier | Acyl group | ||
| Cyanocobalamine | Methylcobalamine &Deoxyadenosylcobalamine | Transfer of H2 group & isomerization | Alkyl group or hydrogen atom | ||
| Biotine | Biocytin | Carboxylation reaction | Carbon dioxide | ||
| Thiamine(Vit B1) | Thiamine Pyrophosphate(TPP) | Oxidtive Decarboxylation & transketolase reaction | Hydroxy-ethyl | ||
Metalloenzymes (Cofactors)- b) For transfer of hydrogen- Lippoic acid
| Metal | Metalloenzymes |
| Copper (Cu+2/Cu+) | Cytochrome oxidase, Lysyl oxidase, ceruloplasmin |
| Iron (Fe+2/Fe+) | Xanthine oxidase |
| Zinc (Zn+2) | Carbonic anhydrase, alkaline phosphatase, alcohol dehydrogenase, carboxypeptidase, glutamate dehrdogenase, lactate dehdrogenase, superoxide dismutase |
| Magnesium (Mg+2) | Phosphatases, kinase, glutathione synthase |
| Selenium | Glutathione peroxidise |
| Molybdenum | Xanthine oxidase, sulphite oxidase |
Exam Important
- Co- substrates- In a group transfer reaction coenzyme acts either a donar or acceptor. Most common mechanism of coenzymes.
- Non protein- chemical components are organic molecules(coenzyme)
- Classification of coenzymes-For transfer of hydrogen- Lippoic acid
- Zinc- carbonic anhydrase, Alcohol dehydrogenase
- Transketolase reactions require thiamine pyrophosphate (TPP).
- Riboflavin and niacin are involved in redox (reduction and oxidation) reactions.
- Two important enzymes using molybdenum are xanthine oxidase and sulfite oxidase.
-
Metalloenzymes (Cofactors)-
Metal Metalloenzymes Copper (Cu+2/Cu+) Cytochrome oxidase, Lysyl oxidase, ceruloplasmin Iron (Fe+2/Fe+) Xanthine oxidase Zinc (Zn+2) Carbonic anhydrase, alkaline phosphatase, alcohol dehydrogenase, carboxypeptidase, glutamate dehrdogenase, lactate dehdrogenase, superoxide dismutase Magnesium (Mg+2) Phosphatases, kinase, glutathione synthase Selenium Glutathione peroxidise Molybdenum Xanthine oxidase, sulphite oxidase -
Vitamin Coenzyme Function as Coenyme Entity transferred Riboflavin (Vit B2) FAD, FMN Oxidation & reduction reaction Hydrogen atoms Niacin NAD+, NADH+ Oxidation & reduction rxn Hydride ion Coenzyme for pyruvate dehydrogenase– NADPH
7. Coenzyme for Glucose-6 phosphate dehydrogenase- NADP
8. Coenzyme for malate dehydrogenase- NAD+
9. Coenzyme for pyruvate dehydrogenase– NADPH
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