Enzyme cofactors are non-protein molecules required for enzyme activity. There are two main types - loosely bound coenzymes and tightly bound prosthetic groups. Cofactors include vitamins and derivatives, organic molecules like nucleotides, and inorganic ions. They help transfer atoms and groups between substrates in redox, group transfer, and other enzyme-catalyzed reactions. Examples are NAD+/NADP+, FAD, biotin, coenzyme A, thiamine pyrophosphate, and metal ions like iron, copper, and zinc in metalloproteins. Cofactors extend an enzyme's catalytic capability and allow it to function in many critical biochemical pathways.

1. ENZYME COFACTORS
-------COENZYMES
DR RINA DAS MEHTA
MMCP, MULLANA

2. COFACTORS IMPORTANCE
COFACTOR ARE THE NON-PROTEIN, LOW MOLECULAR
COMPOUND OF ENZYME
COFACTOR - A CO-CATALYST REQUIRED FOR ENZYME
ACTIVITY, "HELPER MOLECULES" THAT ASSIST IN BIOCHEMICAL
TRANSFORMATIONS.
APOENZYME - ENZYME LACKING COFACTOR (INACTIVE)
HOLOENZYME - ENZYME WITH COFACTORS (ACTIVE)
CLASSIFICATION:
• LOOSELY-BOUND COFACTORS TERMED COENZYMES
• TIGHTLY-BOUND COFACTORS TERMED PROSTHETIC GROUPS

3. COFACTORS
• ORGANIC COFACTORS
• VITAMINS OR VITAMIN DERIVATIVES (WATER-
SOLUBLE = ALL B VITAMINS, VITAMIN C, LIPID-
SOLUBLE – K, A, E
• HETEROCYCLES WITH THE REST OF THE MOLECULE
OF PHOSPHORIC ACID
• MANY COFACTORS CONTAIN THE NUCLEOTIDE
(AMP) AS PART OF THEIR STRUCTURE
• INORGANIC COFACTORS
• METAL IONS MG2+, CU+, MN2+, ZN2+, SE, IRON-
SULFUR CLUSTERS

4. Cofactor Vitamin Enzyme reaction (example)
Thiamine diphosphate Thiamine, B1 Oxidative decarboxylation
FAD, FMN Riboflavin, B2 Redox reactions (transfer of H+)
NAD+, NADP+ Niacin, B3 Redox reactions (transfer of H+)
Coenzyme A Pantothenic acid, B5 Metabolism of FA (transfer of acyl
groups )
Pyridoxalphosphate Pyridoxine, B6 Transamination, decarboxylation of
AA
Carboxybiotin Biotin, H, B7 Carboxylation (CO2)
Tetrahydrolic acid Folic acid, B9 Transfer of C1
Ascorbic acid Vitamin C Hydroxylation reaction (collagen)
cis-retinal + opsin Retinol, A Electron transport , antioxidant
Tocoferol, E Redox reaction, antioxidant
Menaquinone Vitamin K Transfer of carbonyl group and
electrons
Lipoamide Lipoic acid Transfer of electrons and acyl group
Cobalamine Cobalamine, B12 Izomeration, transfer of methyl group

5. Cofactor Group transferred
Adenosine triphosphate (ATP) Phosphate group
S-adenosylmethionin (SAM) Methyl group
Coenzyme Q Electrons
Cytidine triphosphate (CTP) Diacylglycerols and lipid
head groups
Glutathione Electrons
Heme Electrons
Tetrahydrobiopterin Oxygen atom and electrons

6. CLASSIFICATION OF COFACTORS
BY REACTIONS THAT HELP
CATALYZE
• COFACTORS OF OXIDOREDUCTASES :
• NAD(P)+,
• FAD,
• CYTOCHROMES (CONTAINING HEME),
• FE-S COMPLEXES
• COFACTORS THAT TRANSPORT ONE CARBON RESIDUES:
• TETRAHYDROFOLATE,
• VITAMIN B12,
• S-ADENOSYLMETHIONIN,
• BIOTIN (COFACTOR OF CARBOXYLASES)
• COFACTORS THAT TRANSPORT ACYL GROUP:
• LIPOIC ACID (PROSTHETIC GROUP OF PDH, A-KGDH),
• HSCOA,
• PYRIDOXAL PHOSPHATE (TRANSAMINASES)

7. COFACTORS FOR
OXIDOREDUCTASES
NIKOTINAMIDE ADENINE DINUKLEOTIDE (NAD+)
NIKOTINAMIDE ADENINE DINUKLEOTIDE PHOSPHATE
(NADP+)
PRECURSOR IS NIACIN (VITAMIN B3)
FLAVIN ADENINE DINUCLEOTIDE (FAD)
FLAVIN MONONUCLEOTIDE (FMN)
PRECURSOR IS RIBOFLAVIN (VITAMIN B2)
COENZYME Q
CYTOCHROMS FE3+ + E-  FE2 (CYT A1, CYT A3, CYT
B, CYT C)
CU2+ + E-  CU+ (CYT A)

8. SOME ENZYMES CONTAINING
FAD, FMN
ACYL-COA DEHYDROGENASE
FAD
SUCCINATE DEHYDROGENASE
FAD
GLYCEROL-3-PHOSPHATE
DEHYDROGENASE
FAD

9. COENZYME Q
• PARTICIPATES IN AEROBIC CELLULAR RESPIRATION,
GENERATING ENERGY IN THE FORM OF ATP
• COMPONENT OF THE ELECTRON TRANSPORT CHAIN
• COENZYME Q IN HUMAN MITOCHONDRIA IS COQ10 (Q = THE
QUINON HEAD , 10 = THE NUMBER OF ISOPRENE REPEATS IN
THE TAIL
• HYDROFILIC HEAD IS MOVABLE, IT TRANSFERRES ELECTRONS,
POLYISOPRENE TAIL IS ANCHORED IN THE MEMBRANE..
Reduced form Oxidized form

10. COFACTORS OF TRANSFERASES
ADENOSINE TRIPHOSPHATE (ATP)  PHOSPHATE
GUANOSIT TRIPHOSPHATE (GTP)  PHOSPHATE
PYRIDOXAL PHOSPHATE (PLP)  -NH3
(PYRIDOXINE, VITAMIN B6)
TETRAHYDROFOLATE (THF)  C1-FRAGMENT
(FOLIC ACID, VITAMIN B6)
COENZYME A (COA, HS-CO-A)  ACYL
S-ADENOSYLMETHIONIN (SAM)  ACTIVE
METHYL

11. ATP
• ATP TRANSPORTS CHEMICAL ENERGY WITHIN CELLS FOR
METABOLISM
• SUBSTRATE IN SIGNAL TRANDUCTION PATHWAYS BY
KINASES (TRANSFERASES) THAT PHOSPHORYLATE
PROTEINS AND LIPIDS
• ENERGY STORED IN ATP MAY BE RELEASED UPON
HYDROLYSIS OF THE PHOSPHOANHYDRIDE BONDS
+ P ─ P ─ adenosin (ADP)
+ P ─ adenosin (AMP)
inorganic phosphate (Pi)
inorganic pyrophosphate (PPi)

12. PYRIDOXALPHOSPHATE (PLP)
• PROSTHETIC GROUP OF AMINOTRANSFERASES
• COENZYME IN ALL TRANSAMINATION
REACTIONS, AND IN SOME DECARBOXYLATION
AND DEAMINATION REACTIONS OF AMINO
ACIDS.
Pyridoxine
(vit. B6)
Pyridoxal-5-phosphate (PLP) Pyridoxamine-5-phosphate

13. THIAMINE PYROPHOSPHATE
(DIPHOSPHATE), TPP
• TPP IS AN ACTIVE FORM OF VITAMIN B1 (FIRST DISCOVERED VITAMIN).
• TPP IS CONSIST OF SUBSTITUTED RINGS (PYRIMIDINE, THIAZOLE). HIGHLY
HYDROPHILIC SUBSTANCE.
• TPP CATALYSES THE REVERSIBLE CLEAVAGE OF A SUBSTRATE COMPOUND AT A C ─ C
BOND CONNECTING A C = O GROUP TO AN ADJACENT REACTIVE GROUP (USUALLY A
CARBOXYLIC ACID OR AN ALCOHOL)
• TPP TRANSFERS TWO-CARBON RESIDUES IN THE CYTOPLASMIC TRANSKETOLASE
REACTION IN PENTOSE PHOSPHATE PATHWAY
• OXIDATIVE DECARBOXYLATION REACTION OF Α-KETOACIDS AND FORMATION OF
ALDEHYDES (PYRUVATE → ACETALDEHYDE), COFACTOR OF MULTIENZYME
COMPLEXES (PDH, A-KGDH)

14. TETRAHYDROFOLATE (THF)
• ACTIVE FORM IS TETRAHYDROFOLATE
• FOLATES ARE DONORS OF 1-C UNITS FOR ALL OXIDATION LEVELS
OF CARBON EXCEPT THAT OF CO2
• THF IS COENZYME OF TRANSFERASES. N5,N10-THF TRANSFERS
ONE CARBON UNITS, METHYLENE OR METHENYL
• THIS REACTION IS PART OF THE SYNTHESIS OF NUCLEOTIDES AND
NUCLEIC ACIDS.

15. COENZYME A
• Coenzyme A functions as an acyl group carrier
• A thiol can react with carboxylic acids to form thioesters.
• It assists in transferring fatty acids from the cytoplasm to
mitochondria
• Acetyl coenzyme A (acetyl-CoA) is a macroergic compound
effective in a variety of metabolic reactions (b-oxidation of fatty
acids, biosynthesis of lipids)

16. BIOTIN
• CONDENSATE OF UREA AND THIOFENE + THE
REST OF VALERIC ACID;
• COENZYME IN CARBOXYLATION REACTION
• PROSTHETIC GROUP OF ACETYL-COA
CARBOXYLASE AND OTHER ATP-DEPENDENT
CARBOXYLASES
• COVALENTLY ATTACHED TO APOENZYME BOUND
TO Ε-AMINO GROUP OF LYSINE.

17. LIPOIC ACID
• SATURATED FATTY ACID 8
CARBONS)
• CARBONS 6, 7 A 8 CONSTITUTE
HETEROCYCLE WITH TWO ATOMS OF
SULFUR.
• IS PROSTHETIC GROUP OF ENZYMES,
TRANSMITS HYDROGEN AND AND
ACYL GROUP .
• COVALENTLY ATTACHED TO
APOENZYME - BINDS AN AMIDE
BOND TO Ε-AMINO GROUP OF
LYSINE, WHY IT IS ALSO CALLED
LIPOAMID.
• OXIDATION AND DECARBOXYLATIO
OF A-KETOACIDS (PYRUVATE
DEHYDROGENASE, A-
KETOGLUTARATE DEHYDROGENASE)
• ANTIOXIDANT (REDUCED FORM IS
REGENERATED VIT. C AND VIT. E).

18. VITAMIN A
• VIT. A IS NECESSARY TO FORM
RHODOPSIN (IN RODES) AND
IODOPSIN (IN CONES) - VISUAL
PIGMENT.
• RETINALDEHYD IS A PROSTHETIC
GROUP OF LIGHT-SENSITIVE OPSIN
PROTEIN.
• IN THE RETINA, ALL-TRANS-RETINOL
IS ISOMERIZED TO 11-CIS-RETINOL →
OXIDIZED TO 11-CIS-RETINALDEHYD,
 REACTION WITH OPSIN (LYS) → TO
FORM THE HOLOPROTEIN
RHODOPSIN.

19. Vitamin K1
Vitamin K2
VITAMIN K
• VITAMIN K1 (FYLOQUINONE) –
PLANT ORIGIN
• VITAMIN K2 (MENAQUINONE) –
NORMALLY PRODUCED BY
BACTERIA IN THE LARGE
INTESTINE
• K1 A K2 ARE USED DIFFERENTLY
IN THE BODY
• K1 – USED MAINLY FOR BLOOD
CLOTHING
• K2 – IMPORTANT IN NON-
COAGULATION ACTIONS - AS
IN METABOLISM AND BONE
MINERALIZATION, IN CELL
GROWTH, METABOLISM OF
BLOOD VESSEL WALLS CELLS.
Synthetic derivatives of Vit.K
Fyloquinone
Menaquinone

20. VITAMIN K - FUNCTION
• COFACTOR OF LIVER MICROSOMAL CARBOXYLASE WHICH
CARBOXYLATES GLUTAMATE RESIDUES TO G-
CARBOXYGLUTAMATE DURING SYNTHESIS OF
PROTHROMBIN AND COAGULATION FACTORS VII, IX A X
(POSTTRANSLATION REACTION).
• CARBOXYLATED GLUTAMATE CHELATES CA2+ IONS,
PERMITTING THE BINDING OF BLOOD CLOTTING PROTEINS
TO MEMBRANES.
• FORMS THE BINDING SITE FOR CA2+ ALSO IN OTHER
PROTEINS – OSTEOCALCIN.

21. TOCOFEROL, VITAMIN E
• ALPHA-TOCOPHEROLCHINON FORMED BY
OXIDATION FROM A-TOCOPHEROL IS A
COFACTOR IN THE SYNTHESIS OF
MITOCHONDRIAL UNSATURATED FATTY ACIDS.
Chromanol ring hydrophobic aliphatic side chain

22. VITAMIN E AS ANTIOXIDANT
• STOPS FREE RADICAL REACTIONS (PEROXYL RADICALS ROO , OXYGEN
RADICALS HO, LIPOPEROXID RADICALS LOO). CHROMANOL RING
WITH OH GROUP → UPTAKE RADICALS
O
HO

23. VITAMIN C
• HYDROXYLATION OF PROLINE AND LYSINE (COLLAGEN)
• SYNTHESIS OF COLLAGEN – PROLYLHYDROXYLASE,
LYSYLHYDROXYLASE A LYSYLOXIDASE CONTAINE FE2+
AND ASCORBATE AS COFACTORS.
• METABOLISM OF TYR IN BRAIN
• FE MOBILIZATION FROM SPLEEN
• MAY PREVENT THE TOXIC EFFECTS OF SOME METALS
• AMELIORATES ALLERGIC RESPONSES
• CAN STIMULATE THE IMMUNE SYSTEM
• VITAMIN C IS A REASONABLY STRONG REDUCING AGENT
• IT FUNCTIONS AS AN ELECTRON CARRIER

24. IONS AS A COFACTORS
Ion Examples of enzymes containing this ion
Cu2+ Cytochromoxidase, catalase
Fe2+ a Fe3+ Cytochroms, hydroxylases
Mg2+ Glucose-6-phosphatase, hexokinase, DNA-
polymerase,
Mn2+ Arginase
Zn2+ Alcohol dehydrogenase, DNA polymerase,
carboanhydrase
Se Glutathionperoxidase
FeS proteins (Fe2S2) NADH dehydrogenase, succinate dehydrogenase

25. FERREDOXINS
• FES PROTEINS – FERREDOXINS - FE2S2, FE4S4
ELECTRON TRANSFER :
• REDOX REACTION IN MITOCHONDRIAL RESPIRATORY
CHAIN (COMPLEX I AND COMPLEX II)
• NADH DEHYDRODENASE, KOENZYM Q - CYTOCHROM C
REDUCTASE, SUCCINATE – KOENZYM Q REDUCTASE

26. METALLOPORPHYRINS - HEME
• ORGANIC, CYCLIC COMPOUNDS
DERIVED FROM THE TETRAPYRROLE
- PORPHYRIN - FOUR PYRROL RINGS
ARE LINKED WITH METHYLENE
BRIDGES.
• COMPLEXES WITH METAL IONS
• HEME – FE, OXYGENE
TRANSPORT
• CHLOROPHYL – MG,
PHOTOSYNTHESIS

27. METALLOPORPHYRINS -
COBALAMIN (VITAMIN B12)
• CHEMICALLY MOST COMPLEX
VITAMIN
• STRUCTURALLY SIMILAR TO HEME
- COMPLEX OF ORGANIC
COMPOUNDS, ATOM WITHIN THE
MOLECULE IS CO,
• IN MAN THERE ARE TWO
METABOLICALLY ACTIVE FORMS:
METHYLKOBALAMIN AND
ADENOSYLKOBALAMIN.
• COBALAMIN CATALYSES TWO
REACTIONS
• CYTOPLASMIC METHYLATION
OF HOMOCYSTEIN TO
METHIONIN.
• MITOCHONDRIAL
METHYLMALONYL-COA
MUTASE (METHYLMALONYL-
COA → SUKCYNYL-COA)
NEEDS DEOXY
ADENOSYLKOBALAMIN.