happy5
Forum Junior
Topics: 10
Posts: 24
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From NBME 1:
Neutrophils produce reactive oxygen compounds following the phagocytosis of bacteria. Which of the following enzymes protects body tissues against these highly reactive oxygen compunds>
a. cyclooxygenase
b. lipoxygenase
c. myeloperoxidase
d. superoxide dismutase
e. xanthine oxidase
Ok, so obviously it is C or D. A friend told me it is C, but I don't understand why 
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| jamdoc
Forum Elite
Topics: 30
Posts: 244
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answer is D.
its not C bcoz myeloperoxidase catalyses in formation of Hypochlorous acid from hydrogen peroxide which aids in killing microbes.
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| NE
Forum Guru
Topics: 53
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SOD protects cells from DNA damage, lipid peroxidation, ionizing radiation damage, protein denaturation, and many other forms of progressive cell degradation.
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| vallia
Forum Guru
Topics: 98
Posts: 889
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D
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| 10+from_medgrad
Forum Junior
Topics: 6
Posts: 25
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Three groups of enzymes play significant roles in protecting cells from oxidant stress:
Superoxide dismutases (SOD) are enzymes that catalyze the conversion of two superoxides into hydrogen peroxide and oxygen. The benefit here is that hydrogen peroxide is substantially less toxic that superoxide. SOD accelerates this detoxifying reaction roughly 10,000-fold over the non-catalyzed reaction.
SODs are metal-containing enzymes that depend on a bound manganese, copper or zinc for their antioxidant activity. In mammals, the manganese-containing enzyme is most abundant in mitochondria, while the zinc or copper forms predominant in cytoplasm. Interestingly, SODs are inducible enzymes - exposure of bacteria or vertebrate cells to higher concentrations of oxygen results in rapid increases in the concentration of SOD.
Catalase is found in peroxisomes in eucaryotic cells. It degrades hydrogen peroxide to water and oxygen, and hence finishes the detoxification reaction started by SOD.
Glutathione peroxidase is a group of enzymes, the most abundant of which contain selenium. These enyzmes, like catalase, degrade hydrogen peroxide. They also reduce organic peroxides to alcohols, providing another route for eliminating toxic oxidants.
In addition to these enzymes, glutathione transferase, ceruloplasmin, hemoxygenase and possibly several other enzymes may participate in enzymatic control of oxygen radicals and their products.
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