Nos1

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Location

The human gene NOS1, found on chromosome 12, encodes for a nitric oxide synthase. Nitric oxide synthases consume L-arginine to produce nitric oxide. The chemical equation is shown below.

2 L-arginine + 3 NADPH + 4 O(2) = 2 L- citrulline + 2 nitric oxide + 3 NADP(+) + 4 H(2)O

Nitric oxide is used in a wide variety of processes. A few examples of molecular processes include heme binding, NADP binding, calcium signaling, and oxidation-reduction reactions. Biological examples include regulation of cardiac muscle contraction, blood coagulation, aging, and regulation of neurogenesis. There are five known isoforms known for NOS1 in humans produced by alternative splicing, which are expressed at different levels as denoted by microarray data. Please note that microarray data is only available for isoforms 1, 3, and 4.

Tissue Isoform 1 Isoform 3 Isoform 4

Skeletal muscle Moderate N/A Moderate Brain Moderate N/A Low Testis Moderate Moderate Moderate Lung Moderate N/A Moderate Kidney Moderate N/A Moderate Heart Low N/A N/A Adrenal gland Low N/A N/A Retina Low N/A N/A

Image:Expression table snip.jpg

Function

Disease

Relevance

Structural highlights

Nos exists as a homodimer. This homodimer consists of two regions. One region is an N-terminal oxygenase domain and the other is a C-terminal reductase. The N-terminal oxygenase domain is an extended beta sheet cage with binding sites for heme and pterin. Nos has a N-terminal catalytic domain with a heme active site. Nos 1 also has a cofactor site nearby for tetrahydrobiopterin (H4B). Nos has a C-terminal reductase domain containing FMN, FAD and NADPH binding sites. Electrons are passed from FAD to FMN and then to the heme. This electron flow is controlled by the binding of CaM and Ca2+ in the linker region between the two major domains. The linker between the oxygenase and reductase domains contains a calmodulin-binding sequence. Nos1 is found in neuronal tissue.

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