Elsevier Inc. NAD precursor, metabolite transport NADH shuttle Nnt Nadk2 Nadk NADH NADPH NADP+ NAD+ nicotinamide adenine dinucleotide utilization pathway nicotinamide adenine dinucleotide biosynthetic pathway NADH shuttle ---> NADH NAD precursor, metabolite transport ---> nicotinamide adenine dinucleotide biosynthetic pathway NAD precursor, metabolite transport ---> NAD+ NAD+ ---> nicotinamide adenine dinucleotide utilization pathway NAD+ ---> NADP+ NADPH <--> NADP+ NAD+ <--> NADH NADP+ ---> NADPH NADH ---> NAD+ nicotinamide adenine dinucleotide biosynthetic pathway ---> NAD+