Nicotinamide and Flavin Coenzymes

Nicotinamide and Flavin Coenzymes.—High-frequency (220 MHz) H n.m.r. spectroscopy shows that there are differences in conformation between oxidized and reduced pyridine coenzymes. A preliminary report on the P n.m.r. spectra of NAD+ and NADH confirms these observations, as the spectrum of NAD+ consists of an AB quartet while there is only a single resonance discernible in the spectrum of NADH. 

Catalysis by flavoenzymes has been reviewed and various analogues of FAD have been prepared e.g. P -adenosine-P -riboflavin triphosphate and flavin-nicotinamide dinucleotide ) which show little enzymic activity. The kinetic constants of the interaction between nicotinamide-4-methyl-5-acetylimidazole dinucleotide (39) and lactic dehydrogenase suggest the presence of an anionic group near the adenine residue at the coenzyme binding site of the enzyme.  

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Pantothenic acid, sometimes called vitamin B3, is a vitamin that makes up one part of a complex coenzyme called coenzyme A (CoA) (Figure 18.23). Pantothenic acid is also a constituent of acyl carrier proteins. Coenzyme A consists of 3, 5 -adenosine bisphosphate joined to 4-phosphopantetheine in a phosphoric anhydride linkage. Phosphopantetheine in turn consists of three parts /3-mercaptoethylamine linked to /3-alanine, which makes an amide bond with a branched-chain dihydroxy acid. As was the case for the nicotinamide and flavin coenzymes, the adenine nucleotide moiety of CoA acts as a recognition site, increasing the affinity and specificity of CoA binding to its enzymes. 

Purine and pyrimidine nucleotides are key components of all living cells on Earth, and are required for the synthesis of essential cofactors like the nicotinamide and flavine coenzymes and CoA as well as of vitamins like thiamin. Moreover, they are involved in the synthesis of secondary metabolites and are regulators of the synthesis... 

Coupled chemoenzymatic transfer hydrogenation catalysis for enantioselective reduction and oxidation reactions. Tetrahedron Asymmetry, 16, 3512-3519 (g) Hollmaim, F., Witholt, B., and Schmid, A. (2002) (Cp Rh(bpy) (H20)) " a versatile tool for efficient and non-enzymatic regeneration of nicotinamide and flavin coenzymes. 

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