Co-Enzymes

Co-EnzymesEnzymes sometimes are conjugated

proteinsEnzyme (conjugated protein)=Apo-enzyme (inactive)The non-protein part = Co-enzyme

Apo-enzyme + Co-enzyme=Holoenzyme (active)

Apo-Enzyme and Co-EnzymeSome enzymes have two partsThe protein part is called

ApoenzymeThe non-protein part is called Co-

enzymeWhen tightly bound the Co-enzyme is

called Prosthetic-Group

Classification of Co-Enzymes

Coenzymes can be classified by two ways

( I ) Classification based on functional characteristics

(II ) Classification based on structure

(I) Classification based on functional characteristicsA. Transfer of group other than H 1. Sugar Phosphates 2. Thiamine pyro-phosphates 3. Pyridoxal Phosphate 4. Folate co-enzyme 5. Co-enzyme A 6.Biotin 7.Cobamide co-enzyme B12

8.Lipoic Acid

B. Transfer of H+ group

1. NAD+, NADP+

2. FMN , FAD3 LIPOIC ACID4.C0-ENZYME Q

(II) Classification based on structurePresence of Adenine ring

joined to Ribose

Many Co-enzymes may therefore be regarded as derivatives of Adenosine mono phosphate .They are:-

Co-enzymes as Adenosine Derivatives1. Active Methionine 2.Amino Acid Adenylate 3.Active Sulphate 4. 3’ 5’ Cyclic AMP 5. NAD, NADP 6. FAD 7.Co.A

Characteristics Of Co-Enzymes Co-Enzymes are :- Thermo stableDialyzableNon- colloidal Non-proteinAre altered at the end of a reaction and

sometimes may be changedThey usually belong to the Vitamin ‘B’

complex group

Co-Enzyme Vitamin Derivative

Enzyme Requiring

TPPCo-Decarboxylase Vitamin B1

Thiamine

Pyruvate Dehydrogenaseα.Keto Glutarate Dehydrogenase

Transketolase

FAD

FMN

Vitamin B2

(Riboflavin)

D-amino acid Oxidase

L-amino acid Oxidase

Pyridoxal PO4

Co-TransaminaseVitamin B6

Pyridoxine Transaminase

Co-Enzyme Vitamin Derivative

Enzyme Requiring

Co-Enzyme ACo-Acylase

VitaminPantothenic Acid

ThiokinasesThiolases

NAD+

NADP+

VitaminNicotinic Acid

LDH,Alcohol DehydrogenaseG-6-P Dehydrogenase

Tetra Hydro Folate (FH4)

Folic acidOne Carbon Transfers

Thymidilate SynthaseSerine Trans Hydroxy methylase

CobamideCo-enzyme

Vitamin B12Homocysteine methyl Transferase

Co-Enzyme Vitamin Derivative

Enzyme Requiring

BiotinCo-Carboxylase

VitaminBiotin

Acetyl CoA CarboxylasePyru: Carboxylase

Ubiquinone

NADH DehydrogenaseCytochrome b

HemeCo-enzyme

- PeroxidaseCatalaseCytochrome

Function of Co-enzymesThey accept atom or group from a

substrate and transfer it to the other molecule.

Eg: Transaminases

R─NH2 + R1─ C ═ O + PyPO4

PyPO4─NH2

R1─ NH2 + R─ C═ O + PyPO4

NAD and NADP act as hydrogen acceptors in dehydrogenating reactions

T.P.P functions in oxidative decarboxylations.

CoA in Acyl group carrierTetrahydrofolate as formate carrier

in the synthesis of Purines and Pyrimidines.

PROENZYMES

Some enzymes, particularly the Proteolytic enzyme , may be secreted as inactive proenzymes or zymogen.

At the active site ,one or more specific covalent peptide bonds of each such pro-enzymes are hydrolyzed either enzymatically or by pH changes to yield the active enzyme and some inactive peptides called masking substances

Hydrolysis makes the active site of the enzyme free and available to catalytic action.

PROENZYME ACTIVATOR PRODUCTS

Pro-Enzyme

Activator Active Enzyme

Masking Substances

PepsinogenHClor Pepsin

Pepsin Inactive peptide

Trypsinogen

Enterokinase

Trypsin Inactive Hexapeptide

Chymotrypsinogen

Trypsin,Chymotrypsin

α-Chymotrpsin

α-Inactive Peptide

PROENZYME ACTIVATOR PRODUCTSPro-Enzyme Activator Active

EnzymeMasking Substances

Pro-Carboxypeptidase A

Trypsin Carboxypeptidase A

Inactive Peptide

Prothrombin Prothrombinase

Thrombin Inactive polypeptide

Pro-Fibrinolysine

Fibrino lyso Kinase

Fibrino Lysine

InactivePeptide