active oxygen (reactive oxygen species {ROS})

Introduction

Molecular oxygen (O2) exists in the ground state as a triplet. Thus although energetically favorable, oxidation of organic compounds is slow in the absence of catalysis because nearly all organic compounds are singlets & the interaction is forbidden.

1, 2 & 3 electron reduction products of molecular oxygen (hydroxyl radical, hydrogen peroxide & superoxide) & their derivatives obtained from binding to organic compounds (peroxides & hydroperoxides) are much more reactive than molecular oxygen (O2) itself.

Some ROS are also radicals,(hydroxyl radical & superoxide).

ROS are generated in the electron transport chain in mitochondria as a part of normal metabolism & by other oxidoreductases. NOX1, NOXA1, NOXO1, RAC1 & CYBA form a functional multimeric complex supporting ROS production.

ROS participate in a variety of biological processes including host defense, hormone biosynthesis, oxygen sensing & signal transduction.

In susceptible cells, low levels of ROS may lead to apoptosis, but high levels are associated with necrosis.

To protect cells from physiologic & pathologic oxidative stress, antioxidant systems have evolved to keep ROS from reaching cytotoxic levels.

More general terms

• biochemistry

Additional terms

• antioxidant
• oxidative stress