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Co-enzymes and cofactors activity in enzymes

Co-enzymes and cofactors activity in enzymes. Many Enzymes Require Cofactors for Activity. A cofactor is a small non-protein molecules that is bound (either tightly or loosely) to an enzyme and is required for catalysis.

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Co-enzymes and cofactors activity in enzymes

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  1. Co-enzymes and cofactors activity in enzymes

  2. Many Enzymes RequireCofactors for Activity A cofactor is a small non-protein molecules that is bound (either tightly or loosely) to an enzyme and is required for catalysis. Catalytic activity of many enzymes depends on the presence of cofactors.

  3. Many Enzymes RequireCofactors for Activity

  4. Types of cofactors 4

  5. Essential Ion Cofactors • Activator ions – bind reversibly to enzyme and often participate in substrate binding. • Metal ions of metalloenzymes – cations that are tightly bound to enzyme and participate directly in catalysis (Fe, Zn, Cu, Co). • Metal activated enzymes – require or are stimulated by addition of metal ions (i.e. Mg2+, is required by many ATP requiring enzymes)

  6. inorganic cofactors Functions of iron • Ironmust be present in hemoglobin in order to pick oxygen • Electron transport • Oxygen binding • Oxygen carrier

  7. Examples of Iron-dependent Enzymes Aldehyde Oxidase R-CHO + O2 RCOOH + H-O-O-H Tryptophan 5-monooxygenase L-tyrptophan + BH4 + O2 5 OH L-tryptophan + BH2 + H2O Fatty Acid desaturase Stearoyl-CoA + NADH + H+ + O2 Oleoyl-CoA + NAD+ + 2H2O Peroxidase 2H2O2 2H2O + O2 (O2 is either incorporated into the product or reduced by electrons)

  8. Inorganic cofactors Mg2 is used in glycolysis. In the first step of converting glucose to glucose 6-phosphate

  9. Zinc Function • 300 enzymes require zinc • DNA, RNA polymerases • numerous hormones require zinc • insulin • transcription factors (zinc finger proteins) • membrane stability • myelination • skeletal development

  10. Example of metalloenzyme: carbonicanhydrasecontains zinc Example of prosthetic group Metalloenzymescontain firmly bound metal ions at the enzyme active sites (examples: iron, zinc, copper, cobalt).

  11. Coenzyme • Coenzymes are small organic non-protein molecules. • Loosely attached to apoenzymes, seperated easily by dialysis they are often called cosubstrate or secondary substrate. • Reaction involving: • oxidoreduction, • group. transfer, • Isomerization and • covalent bond formation req. coenzyme.

  12. + apoenzyme coenzyme holoenzyme Coenzymes • Organic moleculethat temporarily binds to apoenzyme in order for it to work Non-Protein Total Protein

  13. The functional role of Coenzymes is to act as transporters of chemical group • A coenzyme is a necessary helper for enzymes that assist in biochemical transformations. • These molecules act to transfer chemical groups between enzymes or from Enzyme to substrate or product. • A coenzyme Transport a variety of chemical groups (Such as Hydride, Acetyl, Formyl, Methenyl or methyl).

  14. Vitamin Insufficiency Generally Result in malfunction of enzymes • Main clinical symptoms of dietary vitamin insufficiency generally arise due the malfunction of enzymes. • Dietary vitamin insufficiency leads to a lack of sufficient cofactors derived from vitamins to maintain homeostasis.

  15. Vitamins of B complex group acting as co-enzymes

  16. Vitamin B1 - Thiamine • The active form is thiamin pyrophosphate (TPP) • Thiamin is rapidly converted to thiamin pyrophosphate (TPP) in small intestine, brain and liver. • TPP is formed from thiamin by the action of thiamine diphosphotransferase. • TPP coenzyme is required by enzymes in the decarboxylation of -keto acids. • Entity Transferred; Aldehydes

  17. TPP as co-enzymes

  18. Riboflavin functions, vit B2 Active forms are • Flavin adenine dinucleotide (FAD) • Flavin mononucleotide (FMN) • These play key roles in hydrogen transfer reactions associated with • Glycolysis • TCA cycle • Oxidative phosphorylation. 21

  19. Regulated by ACTH, aldosterone, and thyroid hormone p. 283b

  20. p. 283c

  21. FAD As co-enzyme

  22. Vitamins and Derivatives Involved in Group Transfer Reactions • Nicotine Adenine Dinucleotide (NAD) & Nicotine Adenine Dinucleotide Phosphate (NADP) • Derivative of Niacin (B3) • Serve as cofactors in oxidation / reduction reactions • Act as co-substrates for dehydrogenases • Entity Transferred; Hydride ion (H+ + 2e-) Electron (Hydrogen atom)

  23. H+ (a reaction of glycolysis) glyceraldehyde 3P + NAD (substrate) (co substrate) dehydrogenase (enzyme ) DiPhosphoglyceric acid + NADH (product) (NAD act as co-enzyme & H acceptor)

  24. Coenzyme A (CoA) • Derivative of Pantothenic acid (B5) • Entity Transferred; Acetyl group and other acyl groups

  25. Pyridoxal Phosphate • PLP is Derivative of Pyridoxine (Vit. B6) • involved in : • Transamination reactionsrequired for the synthesis and catabolism of the amino acids. • Decarboxylation reactions. • Entity Transferred; Amino Groups(-NH2)

  26. Example of co-enzyme in amino acid metabolism • Glutamate + pyruvate + pyrodoxal P (co-substrate,acceptor Transaminase & donor of amino group) • (enzyme) α-Ketoglutaric acid + Alanin NH2

  27. Biotin is a coenzyme for enzymes that transfer carboxyl groups • Entity Transferred; Carbon Dioxide

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