NNT (nicotinamide nucleotide transhydrogenase) is a mitochondrial inner membrane enzyme that catalyzes the reversible transhydrogenation between NADH and NADP+, coupled to proton translocation across the membrane 1. The enzyme functions as a proton pump and plays a crucial role in NADPH regeneration, which is essential for maintaining cellular redox homeostasis 2. NNT activity can be enhanced through post-translational modifications, specifically acetylation at lysine 1042, which increases its binding affinity for NADP+ and boosts NADPH production 2. This enhanced NADPH production is critical for iron-sulfur cluster maintenance and cellular protection against oxidative stress and ferroptosis 2. The enzyme also mediates redox-dependent processes beyond metabolism, including skin pigmentation through effects on tyrosinase degradation and melanosome maturation, independent of UV exposure or MITF signaling 1. Genetic variations in NNT are associated with skin color differences in human populations 1. Clinically, NNT deficiency is linked to glucocorticoid deficiency disorders, reflecting its importance in adrenal steroidogenesis and ROS detoxification. The enzyme represents a potential therapeutic target, as its modulation affects cancer cell survival, immune evasion, and pigmentation disorders.