Nicotinamide adenine dinucleotide phosphate supply

Nicotinamide Adenine Dinucleotide Phosphate Supply and Redox Balance... 

Vitamin B5 Niacin (= nicotinic acid) and niacinamide (= nicotinamide) are supplied in the diet and converted in the body into the coenzymes nicotinamide-adenine dinucleotide (NAD) and nicotinamide-adenine dinucleotide phosphate (NADP). These coenzymes are important in tissue respiration. Nicotinic acid can also be formed from tryptophan via kynolin acid. 

In vivo, most electrons from reduced ferredoxin are passed onto nicotinamide adenine dinucleotide phosphate cation (NADP ), via ferredoxin-NADP reductase, to generate the NADPH needed to drive carbon dioxide fixation by the Calvin cycle. Thus electrons from photosystem I can pass through at least three routes (Figure 1), of which route C is preferred (II). However, if the supply of NADP were limited, for example, because of a poor supply of carbon dioxide causing a slow turnover of the Calvin cycle, the electron flow rate along pathway C would be expected to be decreased and more 02" should be made by route B and, to a lesser extent, by route A (15-17), Some oxygen reduction takes place even when carbon dioxide is present in ample amounts (18). 

Transketolase is a TPP-dependent enzyme found in the cytosol of many tissues, especially hver and blood cells, in which principal carbohydrate pathways exist. In the pentose phosphate pathway, which additionally supplies reduced nicotinamide-adenine dinucleotide phosphate (NADPH) necessary for biosynthetic reactions, this enzyme catalyzes the reversible transfer of a glycoaldehyde moiety from the first two carbons of a donor ketose phosphate to the aldehyde carbon of an aldose phosphate. 

The reactions of photosynthesis can be carried out in the dark by cells of green plants if they are provided with a supply both of ATP and of another substance, NADPH (reduced nicotinamide-adenine dinucleotide phosphate), which has the formula... 

Although it was known that the intermediates of the yS-oxidation cycle are chaimelled towards PHA biosynthesis, only recently the precursor sources were identified. In A. caviae, the y3-oxidation intermediate, trans-2-tnoy -CoA is converted to (R)-3-hydroxyacyl-CoA via (R)-specific hydration catalysed by an (R)-specific enoyl-CoA hydratase [125, 126]. Subsequently, Tsuge and co-workers [127] reported the identification of similar enoyl-CoA hydratases in Pseudomonas aeruginosa. In the latter case, two different enoyl-CoA hydratases with different substrate specificities channelled both SCL and MCL enoyl-CoA towards PHA biosynthesis. In recombinant . coli it was further shown that 3-ketoacyl-CoA intermediates in the )8-oxidation cycle can also be channelled towards PHA biosynthesis by a nicotinamide adenine dinucleotide phosphate dependent (NADPH-dependent) 3-ketoacyl-ACP reductase [128]. A similar pathway was also identified in P. aeruginosa [129]. In addition, it was also reported that the acetoacetyl-CoA reductase (PhaB) of R. eutropha can also carry out the conversion of 3-ketoacyl-CoA intermediates in Pathway II to the corresponding (R)-3-hydroxyacyl- CoA in E. coli [130]. The results clearly indicate that several channelling pathways are available to supply substrates from the y3-oxidation cycle to the PHA synthase. This explains why it was not possible to obtain mutants that completely lack PHA accumulation ability, unless the mutation occurred in the PHA synthase gene [131]. 

FIGURE 6.3 Synthesis of 3-Hydroxy-propiorac acid by the malonyl-CoA pathway in recombinant Sacchatxmyces cerevisiae. NADP and NADPH, nicotinamide adenine dinucleotide phosphate. Modified from Chen, Y., Boo, /., Kim, I., Siewers, V., Nielsen, /., 2014. Coupled incremental precursor and co-factor supply improves 3-hydroxypropionic acid production in Saccharomyces cerevisiae. Metabolic Engineering 22,104-109. 

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