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Dual oxidase 1
Dual oxidase 1, also known as DUOX1 or ThOX1 (for thyroid oxidase), is an enzyme which in humans is encoded by the ''DUOX1'' gene. DUOX1 was first identified in the mammalian thyroid gland. In humans, two isoforms are found; hDUOX1 and hDUOX2. Human DUOX protein localization is not exclusive to thyroid tissue; hDUOX1 is prominent in airway epithelial cells and hDUOX2 in the salivary glands and gastrointestinal tract.
== Function ==
Investigations into reactive oxygen species (ROS) in biological systems have, until recently, focused on characterization of phagocytic cell processes. It is now well accepted that production of such species is not restricted to phagocytic cells and can occur in eukaryotic, non-phagocytic cell types via NADPH oxidase (NOX) or dual oxidase (DUOX). This new family of proteins, termed the NOX/DUOX family or NOX family of NADPH oxidases, consists of homologs to the catalytic moiety of phagocytic NADPH-oxidase, gp91phox. Members of the NOX/DUOX family have been found throughout eukaryotic species, including invertebrates, insects, nematodes, fungi, amoeba, alga, and plants (not found in prokaryotes). These enzymes clearly demonstrate regulated production of ROS as their sole function. Genetic analyses have implicated NOX/DUOX derived ROS in biological roles and pathological conditions including hypertension (NOX1), innate immunity (NOX2/DUOX), otoconia formation in the inner ear (NOX3), and thyroid hormone biosynthesis (DUOX1/2). The family currently has seven members including NOX1, NOX2 (formerly known as gp91phox), NOX3, NOX4, NOX5, DUOX1 (this enzyme) and DUOX2.
The current model for ROS generation by ''C. elegans'' DUOX1 (CeDUOX1) proposes that superoxide is generated through reduction of oxygen by two electrons extracted from oxidation of NADPH at the C-terminal NADPH oxidase domain. This unstable superoxide, generated at the extracellular surface, may rapidly convert to hydrogen peroxide and be utilized by the N-terminal peroxidase domain to facilitate tyrosine cross-linking. This model for CeDUOX1 activity was recently supported by a study of two point mutations localized within the peroxidase domain of CeDUOX1; G246D and D392N.〔Meitzler JL, Brandman, R, Ortiz de Montellano, Perturbed heme binding is responsible for the blistering phenotype associated with mutations in the Caenorhabditis elegans dual oxidase 1 (DUOX1) peroxidase domain J. Biol. Chem. 2010, 285, 40991-41000.〕 Both mutations result in a blistering cuticle phenotype, resulting from the loss of tyrosine cross-linking activity. Neither mutant demonstrates a significant decrease in ROS production. These results suggest this peroxidase-like region is directly involved in enzymatic tyrosine cross-linking, but not responsible for ROS production.
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