Nicotinamide adenine dinucleotide phosphate storage

For the formation of one 02 molecule four electrons have to be transferred. This requires a "quantum storage device". In the photosynthetic system of green plants this is achieved with two photosystems that are linked through an electron transport chain, Fig. 10.2, and by means of the thylakoid-membrane that enables the separation of the photoproducts 02 and the reduced form of nicotinamide adenine dinucleotide phosphate, NADPH. 

Several microorganisms are known to accumulate PHB within the cells as an intracellular storage material for carbon and energy source. In microbes PHB synthesis takes place by a sequence of reactions catalyzed by three enzymes— 3-ketothiolase, acetoacetyl-coA reductase and PHB synthase. The first step is catalyzed by the enzyme 3-ketothiolase (E.C. 2.3.1.16) which condenses acetyl-CoA to acetoacetyl-CoA. This intermediate is reduced to D (-)-P-hydroxybutyryl-CoA by an Nicotinamide Adenine Dinucleotide Phosphate (NADPH)-dependent acetoacetyl-CoA reductase (E.C.1.1.1.36) and the enzyme PHB synthase catalyzes the head to tail polymerization of the monomer to PHB (Figure 17.3). 

ATP, ADP, and AMP are agents for the storage and transfer of phosphate groups. Nicotinamide adenine dinucleotide (NAD ) and flavin adenine dinucleotide (FAD) are agents for the storage and transport of electrons in metabolic oxidations and reductions. NAD is a two-electron oxidizing agent... 

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