nitric-oxide synthase complex

Definition

Target type: cellularcomponent

A protein complex which is capable of nitric-oxide synthase activity. [GO_REF:0000088, GOC:bhm, GOC:TermGenie, PMID:25417112]

The nitric-oxide synthase (NOS) complex is a multi-protein assembly responsible for the synthesis of nitric oxide (NO), a signaling molecule with diverse physiological functions. The core of the complex is the NOS enzyme, which catalyzes the conversion of L-arginine to L-citrulline and NO. This enzymatic reaction requires several cofactors and prosthetic groups, including tetrahydrobiopterin (BH4), NADPH, flavin adenine dinucleotide (FAD), flavin mononucleotide (FMN), and heme. The NOS complex also includes various regulatory proteins that modulate its activity and subcellular localization.

The precise composition of the NOS complex can vary depending on the NOS isoform (neuronal NOS, endothelial NOS, and inducible NOS) and the cellular context. However, some common components include:

**NOS enzyme:** This is the central component of the complex, responsible for NO synthesis. It is a dimeric protein with two active sites, each containing a heme group and a reductase domain.

**Calmodulin:** This calcium-binding protein acts as a regulatory subunit of NOS, stimulating its activity upon binding to calcium ions.

**Calmodulin-binding protein:** This protein interacts with calmodulin, facilitating its association with the NOS enzyme.

**Other regulatory proteins:** Various other proteins, such as heat shock proteins, chaperones, and scaffolding proteins, can associate with the NOS complex, contributing to its stability, localization, and activity regulation.

The cellular component of the NOS complex can be localized to various cellular compartments, including the cytoplasm, plasma membrane, endoplasmic reticulum, and mitochondria. Its precise localization is determined by the specific NOS isoform, the cellular context, and the presence of regulatory proteins. For example, neuronal NOS is predominantly localized to the postsynaptic density of neurons, while endothelial NOS is primarily associated with the plasma membrane of endothelial cells.

The NOS complex is a dynamic assembly that can undergo changes in composition, conformation, and localization in response to cellular signaling events. This dynamic nature allows for precise regulation of NO production in response to various stimuli, ensuring appropriate physiological responses.

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Proteins (1)

Compounds (2)