NADP-dependent glucose-6-dehydrogenase

Enzymatic reactions that cannot be monitored directly by spectroscopic changes can be coupled to other reactions that do show such changes. One of the classic examples is the detection of glucose by an assay which depends on its conversion by hexo-kinase into glucose 6-phosphate, which is then coupled to an ancillary indicator reaction with NADP+ and glucose 6-phosphate dehydrogenase ... 

Since, in the microsomal membrane, two NADP+-dependent dehydrogenases are present that catalyze the sequential oxidation of glucose-6-phosphate (G6P) to ribulose-5-phosphate ... 

The first step in the HMP pathway (Fig. 17.6) is the oxidation of glucose-6-phosphate by an NADP+-dependent dehydrogenase. The product, 6-phospho-gluconolactone, is converted to 6-phosphogluconic acid by a lactonase. A second oxidative step mediated by 6-phosphogluconic acid dehydrogenase. 

A localized approach, but one with system-wide impact was reported by Martinez et al. [18], They replaced the native NAD-dependent glyceraldehyde 3-phosphate dehydrogenase, which is a glycolytic enzyme, with a NADP-dependent alternative from Clostridium acetobutylicum. When considered on paper, the replacement increases the stoichiometry of NADPH formation from glucose. To test the altered host cell, synthesis of lycopene and epsilon-caprolactone in the modified strain was compared to the unmodified strain. The modified strains exhibited higher productivity than the parent strains. Flux determinations indicated a reduced reliance on the HMP pathway, which further affirmed the impact of the enzyme change. 

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