Function & Metabolic Role of Coenzymes

Metabolic role of adenosylcobalamine

Prosthetic group

Reaction type of adenosylcobalamin

Mutase reactions

Example of enzyme that adenosylcobalamin aids

Methylmalonyl-CoA mutase

Methylmalonyl-CoA -> succinyl CoA

Metabolic role of ATP

Cosusbtrate

Reaction type of ATP

Group transfer

Groups transfered by ATP

• Phosphoryl (Pi)

• Pyrophosphoryl (PPi)

• Adenylyl (AMP)

• Adenosyl

Reaction types of biotin

• ATP-dependant carboxylation

• Group transfer

Metabolic role of biotin

Prosthetic group

Reactive center of biotin

N1 (left)

Example of enzyme that biotin aids

Pyruvate carboxylase

How is biotin bound to an enzyme

Via amide bond on lysine

Metabolic role of CoA

Cosubstrate

Reaction type of CoA

Acyl group transfer

How is CoA bound to acyl group to make Acetyl-CoA?

Via thioester bond

Reactive centre of CoA

Thiol group on 2-mercaptoethylamine

Reaction type of cytochromes

1 electron reduction at Fe3+

Metabolic role of lipoamide

Prosthetic group

3 enzymes that lipoamide is a prosthetic group for

• Dihydrolipoamide acyltransferase

• Pyruvate dehydrogenase complex

• a-ketoglutarate dehydrogenase complex

Reaction types of lipoamide

• Oxidation of hydroalkyl group from TPP

• Acyl group transfer

How is lipoamide bound to enzyme?

Via amide bond of lysine

Metabolic role of methylcobalamin

Prosthetic group

Reaction type of methylcobalamin

Methyl group transfer

Enzyme that methylcobalamin aids

Homocysteine methyltransferase

Homocysteine -> methionine

Metabolic role of nicotinamide coenzymes

Cosubstrate

Enzymes that nicotinamides are cosubstrates for

Dehydrogenases

Reaction type of nicotinamide coenzymes

Transfer of two electrons (and a proton)

Type of reaction NADPH most often used for

Biosynthesis

Metabolic role of PLP

Prosthetic group

Reaction type of PLP

Transfer of groups to/from amino acids

Example mechanism of PLP

Transamination between amino acid and a-keto acid

Metabolic role of protein coenzymes

Prosthetic group

Three groups that protein enzymes are prosthetic groups for

• Heme

• Metal ions

• Iron-sulphur clusters

Reaction types of protein coenzymes

• Group transfers

• Redox reactions

Metabolic role of riboflavin coenzymes

Prosthetic group

Enzymes that ribos are prosthetic groups for

Oxidoreductases

Reaction type of ribos

1 or 2 electron transfers

Metabolic role of SAM

Cosubstrate

Reaction type of SAM

Group transfer for biosynthesis

Group transfered by SAM

Methyl

What does SAM react with?

Nucleophilic acceptor

Metabolic role of THF

Cosubstrate

Reaction type of THF

Group transfer

Groups that THF transfer

1C subs for thymine methylation

(formyl/hydroxymethyl)

How is THF bound to the enzyme?

Via polyglutamate tail

Example reaction of THF

DNA synthesis

Metabolic role of TPP

Prosthetic group

Enzymes that TPP is a prosthetic group for

• Decarboxylases

• Oxidative decarboxylases

• Transketolases

Reaction type of TPP

Group transfer

Groups transfered by TPP

• 2C carbonyl fragments

• CO₂

Metabolic role of ubiquinone

Cosubstrate

Reaction type of ubiquinone

Electron transfer

Number of electrons transferred by ubiquinone

1 or 2

Example where ubiquinone is found

Electron transfer chain

Metabolic role of UDP

Cosusbtrate

Reaction type of UDP

Group transfer

What group does UDP transfer?

Glycosyl

What process is UDP involved in?

Carbohydrate metabolism

Metabolic role of retinal

Prosthetic group

What is retinal a prosthetic group for?

Rhodopsin

Function of retinal

Photon absorption causes trans -> cis change for vision impulse

Active form of Vitamin D3

1,25-dihydroxycholecalciferol

Role of 1,25-DHC

Ca²⁺ utilisation

Effect of Vit. D3 deficiency

Rickets

Role of vitamin E

Antioxidant

Metabolic role of vitamin K

Prosthetic group

What is vitamin K a prosthetic group for?

Mammalian carboxylase

Reaction type of vitamin K

Carboxylation of coagulant glutamates

Process that vitamin K is involved in

Coagulation