Principles of Biochemistry Volume 2 - A. Lehninger 1985

Bioenergetics and Metabolism
Electron Transport, Oxidative Phosphorylation, and Regulation of ATP Synthesis
Incomplete reduction of oxygen leads to cellular damage

It is crucial for The Cell that an oxygen molecule acquires four electrons and is completely reduced to two molecules of H2O. Incomplete reduction of oxygen, involving The addition of only two electrons, yields hydrogen peroxide (H2O2), whereas the addition of a single electron produces the superoxide radical (:O2). Both hydrogen peroxide and superoxide are extremely toxic to Cells because they damage cellular membranes by reacting with unsaturated fatty acid residues of Membrane Lipids. Aerobic cells protect themselves against this harmful action of superoxide and peroxide using two Enzymes: superoxide dismutase (a metalloenzyme that converts the superoxide radical into hydrogen peroxide) and catalase (which converts hydrogen peroxide into H2O and molecular oxygen)

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Toxic hydrogen peroxide, however, finds a unique application in bombardier beetles. These beetles possess a specialized gland divided into two compartments: one stores a concentrated solution of hydrogen peroxide, and the other contains a solution of hydroquinone. When threatened, this remarkable insect deters its predator by discharging a boiling-hot (100 ˚С) stream of toxic quinone, which is generated through the instant, explosive oxidation of hydroquinone by hydrogen peroxide.



Last update: 06/08/2026

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