Question

1. Describe two metabolic steps of the metabolic network that can generate NADPH.

Answer 1

1. NADPH is produced from NADP+. The major source of NADPH in animals and other non-photosynthetic organisms is the pentose phosphate pathway, by glucose-6-phosphate dehydrogenase (G6PDH) in the first step. The pentose phosphate pathway also produces pentose, another important part of NAD(P)H, from glucose.

   In oxidative phase, two molecules of NADP+ are reduced to NADPH, utilizing the energy from the conversion of glucose-6-phosphate into ribulose 5-phosphate.
   

2. In enzymology, a ferredoxin-NADP+ reductase (EC 1.18.1.2) abbreviated FNR, is an enzyme that catalyzes the chemical reaction

   2 reduced ferredoxin + NADP+ + H+ 2 oxidized ferredoxin + NADPH
   
   The 3 substrates of this enzyme are reduced ferredoxin, NADP+, and H+, whereas its two products are oxidized ferredoxin and NADPH. It has a flavin cofactor, FAD.
   During photosynthesis, electrons are removed from water and transferred to the single electron carrier ferredoxin. Ferredoxin: NADP+ reductase then transfers an electron from each of two ferredoxin molecules to a single molecule of the two electron carrier NADPH.