Reduced nicotinamide adenine dinucleotide phosphate (NADPH) is an essential electron donor in all eukaryotes, bacteria, and archaea. NADPH is vital for the generation of reactive oxygen species (ROS) and the anti-oxidative defense mechanisms of most organisms. But most importantly, it is also the driving force of most biosynthetic enzymatic reactions, including those responsible for the biosynthesis of all major cell components, such as DNA and lipids[1]. In most organisms, NADPH formation occurs principally by reduction of nicotinamide adenine dinucleotide phosphate (NADP+), catalyzed by NADP+-linked dehydrogenases or by energy-linked hydrogen transfer by means of NAD(P)+ transhydrogenase[2]. Hence, to maintain a sufficient quantity of NADP+ for the generation of NADPH, NADP+ biosynthesis is essential[1].

[1] SK Spaans et al. NADPH-generating systems in bacteria and archaea. Front Microbiol. 2015 Jul 29;6:742.
[2] Y Iwahashi et al. Characterization of NADH kinase from Saccharomyces cerevisiae. J Biochem. 1989 Apr;105(4):588-93.