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NItric Oxide (NO)

  • NO is a free radical gas
  • GAS SECOND MESSENGERS CAN DIFFUSE THROUGH BOTH THE CYTOSOL AND THE PLASMA MEMBRANE
  • this makes them excellent paracrine and autocrine signalling molecules

physiology

  • NO mediates a plethora of functions in the body:
  1. relaxation of vascular and gostrointestinal smooth muscle
  2. inhibition of platelet aggregation
  3. reduction of cardiac hypertrophy
  4. protection against ischemia/reperfusion damage of the heart
  5. improvement in cognitive function

toxicity

  • NO is a free radical
  • it can react with the superoxide anion to give peroxoynitrate and then hydroxyl radicals, the latter are very reactive and toxic- used in macrophages
  • it can also bind to non-haem iron in proteins irreversibly, leading to destrution of the proteins
  • many of these are in the mitochondira, leading to cell death

Biosynthesis

  • Nitric Oxide Synthase (NOS) enzymes
  • catalyse the production of NO from L-arginine

NO synthase isozymes

  • neronal NOS 

-nervous system and skeletal system (type II)

- cell communication

  • endothelial NOS

- endothelium 

-vasodilation 

  • inducible NOS

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