NADH reductase is an enzyme that plays a crucial role in cellular respiration. It facilitates the transfer of electrons from NADH to other molecules, helping to generate energy in the form of ATP. This process occurs in the mitochondria, where the enzyme is part of the electron transport chain. The activity of NADH reductase is essential for maintaining the balance of NAD+ and NADH in cells. By converting NADH back to NAD+, it ensures that the cell has enough of this coenzyme to support various metabolic processes, including the Krebs cycle and fatty acid synthesis.