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14 .1 The Chemistry in Vitamins and Coenzymes

Main Menu. 14 .1 The Chemistry in Vitamins and Coenzymes. Nicotinamide Adenine Dinucleotide (NAD + ). Coenzyme (co-substrate) or cofactor in redox reactions. Niacinamide Nicotinamide. Niacin (Vitamin B 3 ) Nicotinic acid.

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14 .1 The Chemistry in Vitamins and Coenzymes

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  1. Main Menu 14.1 The Chemistry in Vitamins and Coenzymes

  2. Nicotinamide Adenine Dinucleotide (NAD+) Coenzyme (co-substrate) or cofactor in redox reactions Niacinamide Nicotinamide Niacin (Vitamin B3) Nicotinic acid Isoniazid , also known as isonicotinylhydrazine (INH), is an organic compound that is the first-line medication in prevention and treatment of tuberculosis. NAD+

  3. The Chemistry of NAD+ Coenzyme (co-substrate) or cofactor in redox reactions NAD+ NADH 2 e- + H+ Electron-deficient aromatic ring Loss of aromaticity Often involved in C=O processes The redox reactions can be reversible. It is a 2-electron transfer process.

  4. The Mechanism of NAD+ Coenzyme (co-substrate) or cofactor in redox reactions NAD+ NADH

  5. Flavin Adenine Dinucleotide (FAD) Coenzyme (co-substrate) in redox reactions Ribitol from reduction of ribose. Riboflavin (vitamin B2) FAD Flavin mononucleotide (FMN) A solution of riboflavin Flavin (from Latin flavus, "yellow")

  6. The Chemistry of FAD Coenzyme (co-substrate) in redox reactions FADH. FAD FADH2 e- + H+ e- + H+ Often involved in C=C processes The redox reactions can be reversible. It can be a 2-electron or 1-electron transfer process.

  7. The Mechanism of FAD Coenzyme (co-substrate) in redox reactions FADH. FAD FADH2

  8. Transfer of acyl groups Coenzyme A (CoA, CoA-SH) Pantothenic acid (vitamin B5) Coenzyme A Various metabolic pathways pKa = 9-10 Mechanisms are similar to Fischer esterification and transesterification.

  9. Cofactor for pyruvatedehydrogenase and a-ketoglutaratedehydrogenase Thiamine or Vitamin B1 thiamine pyrophosphate (TPP) The positive charge of thiazole makes the H more acidic.

  10. Thiamine pyrophate (TPP), lipoamide and FAD are the catalytic cofactors. Mechanism of PyruvateDehydrogenase Lipoic acid lipoamide covalently attached to a Lys of the protein. Mechanism: pyruvate Nucleophilic addition toward C=O Electron deficient (electron sink)

  11. Mechanism of PyruvateDehydrogenase decarboxylation Similar to the transesterification Regenerate TPP Similar to the formation of hemiketal Acetyl CoA

  12. Consume NAD+ and generate NADH Mechanism of PyruvateDehydrogenase regenerated lipoamide (oxidized form) Summary

  13. Common cofactor for aminotransferases Pyridoxal Phosphate (PLP) or Vitamin B6 PLP Isomerization of C=N Pyridoxamine phosphate (PMP) Formation of imine (Schiff base)

  14. Main Menu 1. NAD+ is a common co-enzyme involved in biological redox (reduction/oxidation) processes. Without specifying the R group, which nicotinamide (circled) group is aromatic? Learning Check (a) The one circled in NAD+ because there are 6 p electrons in the aromatic ring. (b) The one circled in NADH because there are 6 p electrons in the aromatic ring. (c) The one circled in NAD+ because there are 10 p electrons in the aromatic ring. (d) The one circled in NADH because there are 10 p electrons in the aromatic ring. (e) None of the above

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