Nitric Oxide

Introduction

Nitric oxide (NO) is an important signalling molecule that acts in many tissues to regulate a diverse range of physiological and cellular processes. It's role was first discovered by several groups who were attempting to identify the agent responsible for promoting blood vessel relaxation and regulating vascular tone. This agent was termed endothelium-derived relaxing factor (EDRF), and was initially assumed to be a protein like most other signalling molecules. The discovery that EDRF was in fact nitric oxide - a highly reactive gase- has led to an explosion of interest in this field, resulted in over 60,000 papers published in the last ten years and won the Nobel prize in 1998. Nitric oxide has now been demonstrated to play a role in a variety of biological processes including neurotransmission, immune defence, the regulation of cell death (apoptosis) and cell motility. Nitric oxide is a short-lived, highly reactive molecule (with a half-life of a few seconds) that is produced from a group of enzymes known as nitric oxide synthases (NOS).

Since it is such a small molecule NO is able to diffuse rapidly across cell membranes and, depending on the conditions, is able to diffuse distances of more than several hundred microns. The biological effects of NO are mediated through the reaction of NO with a number of targets such as haem groups, cysteine residues and iron and zinc clusters. Such a diverse range of targets for NO helps explain the wide range of roles that it plays. Due to the importance of NO, abnormal regulation or control of NO synthesis is capable of affecting a number of important biological processes and has been implicated in a variety of diseases.

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