Superoxide-generating oxidase in phagocytes

What enzyme complex generates superoxide in phagocytes?

NADPH oxidase

What is the primary reaction catalyzed by NADPH oxidase?

NADPH + 2 O₂ → NADP⁺ + H⁺ + 2 O₂⁻.

What is the purpose of superoxide generation in phagocytes?

Microbicidal activity — killing engulfed pathogens

What is the respiratory burst?

A rapid increase in O₂ consumption and ROS production during phagocytosis.

Which ROS are produced downstream of superoxide?

H₂O₂, OH·, singlet oxygen, hypochlorous acid (HOCl), chloramines.

Which enzyme converts H₂O₂ + Cl⁻ → HOCl?

Myeloperoxidase (MPO).

What membrane‑bound component is essential for NADPH oxidase?

Cytochrome b₅₅₈, a heterodimer of gp91ᵖʰᵒˣ and p22ᵖʰᵒˣ.

What cytosolic components translocate during activation?

p47ᵖʰᵒˣ, p67ᵖʰᵒˣ, p40ᵖʰᵒˣ, and Rac (a small GTPase).

What is the electron donor for NADPH oxidase?

NADPH, supplied by the hexose monophosphate shunt.

What triggers assembly of the NADPH oxidase complex?

Phagocyte activation via receptor signaling (e.g., fMet‑Leu‑Phe, C5a, PAF, LTB₄).

What is the first step after receptor binding?

Activation of G‑proteins (pertussis‑toxin‑sensitive GN proteins).

Which second messengers are produced via phospholipase C?

IP₃ and diacylglycerol (DAG).

What does IP₃ do?

Releases Ca²⁺ from intracellular stores.

What does DAG activate?

Protein kinase C (PKC).

What is the role of PKC in oxidase activation?

Phosphorylates p47ᵖʰᵒˣ, enabling cytosolic components to translocate to the membrane.

What are key physiological stimuli for neutrophils?

fMet‑Leu‑Phe, C5a, PAF, LTB₄, IL‑8/NAP‑1.

What type of receptor is the formyl peptide receptor?

A 7‑transmembrane GPCR

What is the affinity (Kₐ) of formyl peptide receptors?

~20 nM in intact cells; 1–2 nM in isolated membranes.

What is chemotaxis vs. respiratory burst sensitivity?

Chemotaxis occurs at lower agonist concentrations; respiratory burst requires higher levels.

Does oxidase activation always require Ca²⁺?

No — there are Ca²⁺‑independent pathways.

What evidence shows Ca²⁺ is not always required?

PMA‑primed cells activate oxidase before Ca²⁺ rises; permeabilized cells show Ca²⁺‑independent activation.

Which phospholipases contribute to oxidase activation?

PLC, PLD, and possibly PLA₂.

What does PLD generate?

Phosphatidic acid, another activator of PKC and signaling pathways.

What is CGD?

An inherited disorder where phagocytes cannot generate superoxide.

What causes CGD?

Mutations in gp91ᵖʰᵒˣ, p22ᵖʰᵒˣ, or cytosolic oxidase components.

What diseases involve excessive ROS release?

Rheumatoid arthritis, ischemia‑reperfusion injury, stroke, myocardial infarction, ARDS.

Which non‑phagocytic cells can generate small amounts of superoxide?

B lymphocytes, fibroblasts, endothelial cells.

What might be the role of oxidase in B cells?

Possible roles in antigen processing, mutation, or immunomodulation.