Given the essential nature of NAD+ in hundreds of biochemical reactions, including glycolytic and mitochondrial energy production, it seems intuitive that any change in concentration could have major consequences.

However, this question has proven surprisingly difficult to answer, in part due to the compartmentalization and protein binding properties of NAD+. Because the concentration of the free nucleotide varies throughout the cell, and the activities of many NAD+ consuming enzymes may be modulated by other factors including local NAD+/NADH redox state, feedback inhibition from nicotinamide, binding partners, or post-translational modifications, simply measuring the in vitro Km of specific consumers for NAD+ and comparing to the concentration measured in tissue homogenates is not sufficient to understand whether their activities will be affected by small concentration changes in intact cells or tissues.