Peroxisomes are membrane-enclosed organelles containing several specific enzymes that promote oxidative reactions. Although peroxisomes are present in most cells, they are particularly large and active in the liver.
All peroxisomes contain one or more enzymes that promote reactions in which hydrogen is removed from particular organic molecules and transferred to molecular oxygen (O2), thereby oxidizing the molecule and forming hydrogen peroxide (H2O2) in the process. The oxidation of toxic molecules by per-oxisomes in this way is an important function of liver and kidney cells. For example, much of the alcohol ingested in alcoholic drinks is oxidized into acetaldehyde by liver peroxisomes.
The enzyme catalase within the peroxisomes prevents the excessive accumulation of hydrogen peroxide by catalyzing the reaction 2H2O2 ^ 2 H2O + O2. Catalase is one of the fastest acting enzymes known (see chapter 4), and it is this reaction that produces the characteristic fizzing when hydrogen peroxide is poured on a wound.
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