Figure 6.

(Color online) Biosynthesis and localization of poly(P)-dependent human mitochondrial NAD kinase.²⁰⁾ NAD⁺ is incorporated into mitochondria through the human mitochondrial membrane, but NADP⁺ is not. Human NAD kinase (blue circle) and mitochondrial NAD kinase (orange circle) are encoded by human NAD kinase gene on chromosome 1 (ch 1) (blue rectangle) and C5orf33 gene on chromosome 5 (ch 5) (orange rectangle) in human genome, respectively. The exon/intron structure and splicing process of the two genes are not included in this figure. The product C5orf33 (orange circle) of C5orf33 gene is delivered to mitochondria using a mitochondrial transit sequence (brown stick) and functions as poly(P)-dependent mitochondrial NAD kinase. Reactions catalyzed by human NAD kinase and human mitochondrial NAD kinase are given in cytosol and mitochondria, respectively. NADPH formed from NADP⁺ is utilized for elimination of reactive oxygen species (ROS). mt DNA, mitochondrial circular DNA; dotted square, mitochondria; dotted circle, nucleus. See text for further details.