Nitric oxide synthase, inducible (iNOS) is an enzyme that in humans is encoded by the NOS2 gene. Nitric oxide is a reactive free radical which acts as a biologic mediator in several processes, including neurotransmission and antimicrobial and antitumoral activities. This gene encodes a nitric oxide synthase which is expressed in liver and is inducible by a combination of lipopolysaccharide and certain cytokines. Three related pseudogenes are located within the Smith-Magenis syndrome region on chromosome 17. Alternative splicing of this gene results in two transcript variants encoding different isoforms.