Cellular and developmental pathogenesis is the result of complicated cellular processes involving molecular interactions among cells and their intra- and inter-cellular milieus. The characterization of molecular interactions in different steps of disease-related metabolic pathways is necessary to understand how abnormalities in these interactions relate to disease and disorders, and how to develop therapeutic strategies to overcome these abnormalities. We focus on kynurenine 3-monooxygenase (KMO) of the kynurenine pathway, which is a metabolic pathway leading to the production of nicotinamide adenine dinucleotide from the degradation of tryptophan.