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BIOLOGICZNE FINKCJE TLENKU AZOTU

Tlenek azotu jest syntezowany przez organizm człowieka z L-argininy, tlenu, NADPH przez liczne syntazy (enzymy) tlenku azotu (ang. Nitric Oxide Synthaze NOS).

Oddychanie przez nos prowadzi do wytwarzania przez ciało tlenku azotu, a oddychanie przez usta sprawia, że tlenek azotu nie jest wytwarzany.

NO is a gaseous signaling molecule.[22] It is a key vertebrate biological messenger, playing a role in a variety of biological processes.[23] It is a bioproduct in almost all types of organisms, including bacteria, plants, fungi, and animal cells.[24]

Nitric oxide, an endothelium-derived relaxing factor (EDRF), is biosynthesized endogenously from L-arginine, oxygen, and NADPH by various nitric oxide synthase (NOS) enzymes.[25] Reduction of inorganic nitrate may also make nitric oxide.[26] One of the main enzymatic targets of nitric oxide is guanylyl cyclase.[27] The binding of nitric oxide to the heme region of the enzyme leads to activation, in the presence of iron.[27] Nitric oxide is highly reactive (having a lifetime of a few seconds), yet diffuses freely across membranes. These attributes make nitric oxide ideal for a transient paracrine (between adjacent cells) and autocrine (within a single cell) signaling molecule.[26] Once nitric oxide is converted to nitrates and nitrites by oxygen and water, cell signaling is deactivated.[27]

The endothelium (inner lining) of blood vessels uses nitric oxide to signal the surrounding smooth muscle to relax, resulting in vasodilation and increasing blood flow.[26] Sildenafil (Viagra) is a drug that uses the nitric oxide pathway. Sildenafil does not produce nitric oxide, but enhances the signals that are downstream of the nitric oxide pathway by protecting cyclic guanosine monophosphate (cGMP) from degradation by cGMP-specific phosphodiesterase type 5 (PDE5) in the corpus cavernosum, allowing for the signal to be enhanced, and thus vasodilation.[25] Another endogenous gaseous transmitter, hydrogen sulfide (H2S) works with NO to induce vasodilation and angiogenesis in a cooperative manner.[28][29]