Reactive Oxygen Species (ROS) and Reactive Nitrogen Species (RNS)

Vocabulary flashcards summarizing key reactive oxygen species (ROS) and reactive nitrogen species (RNS), including their production mechanisms, inactivation pathways, and physiological/pathological effects.

Singlet oxygen ($^1\text{O}_2$)

A reactive oxygen species generated from $\text{O}_2$ by light/photosensitizers or from $\text{H}_2\text{O}_2 + \text{OCl}^-$ in phagocytes. It decays to $\text{O}_2$ with light emission ($1270\,\text{nm}$, $703\,\text{nm}$, $634\,\text{nm}$), is scavenged by carotenoids, and causes photosensitivity, photodegradation, lipid oxidation, and initiation of oxidative reactions.

Superoxide ($^\bullet\text{O}_2^-$)

A reactive oxygen species free radical produced from $\text{O}_2$ in mitochondria during oxidative phosphorylation and by NADPH oxidase in phagocytes. It is inactivated to $\text{H}_2\text{O}_2$ by SOD or reacts with $\text{NO}$ to form $\text{ONOO}^-$, causing local direct oxidation and induction of degradative enzymes.

Hydrogen peroxide ($\text{H}_2\text{O}_2$)

A mild oxidant ROS produced from $^\bullet\text{O}_2^-$ by SOD or by oxidases in peroxisomes. Inactivated by catalase, peroxiredoxin, and GSH peroxidase into $\text{H}_2\text{O}$ and $\text{O}_2$, it participates in cell signaling and is converted by MPO into antimicrobial $\text{OCl}^-$ in phagocytes.

Hydroxyl radical ($^\bullet\text{OH}$)

The most potent, fast-reacting, nonselective oxidant ROS formed slowly from $\text{H}_2\text{O}$ by hydrolysis/radiation or from $\text{H}_2\text{O}_2$ with $\text{Fe}^{2+}$. It diffuses over very short distances and causes major oxidative stress leading to both apoptosis and necrosis.

Nitric oxide ($^\bullet\text{NO}$)

A reactive nitrogen species synthesized from $\text{N}_2$ and $\text{O}_2$ by NOS (e&i) in endothelial cells, WBCs, and neurons, or released by red light ($634\,\text{nm}$). It acts via the cGMP pathway to cause local vasodilation, inhibit leukocyte adhesion, and inhibit Cyt C in mitochondria.

Peroxynitrite ($\text{ONOO}^-$)

A reactive nitrogen species formed rapidly from $\text{NO}$ and $^\bullet\text{O}_2^-$ at high $\text{NO}$ concentrations. It diffuses long distances, causing direct oxidation and radical-mediated nitration reactions that result in major oxidative stress, apoptosis, and necrosis.

Superoxide Dismutase (SOD)

An enzyme present in cytosol, mitochondria, and extracellular spaces that inactivates superoxide ($^\bullet\text{O}_2^-$) by converting it into hydrogen peroxide ($\text{H}_2\text{O}_2$).

Myeloperoxidase (MPO)

An enzyme in phagocytes (PMN) that converts hydrogen peroxide ($\text{H}_2\text{O}_2$) into hypochlorite ($\text{OCl}^-$), a powerful antimicrobial agent.

Carotenoids

Molecules that act as specific scavengers for singlet oxygen ($^1\text{O}_2$) during its inactivation.

Summary Table of Reactive Oxygen and Nitrogen Species

A comprehensive reference detailing production sources, inactivation mechanisms, and biological effects for ROS ($^1\text{O}_2$, $^\bullet\text{O}_2^-$, $\text{H}_2\text{O}_2$, $^\bullet\text{OH}$) and RNS ($^\bullet\text{NO}$, $\text{ONOO}^-$).