Which statement correctly describes the cleavage of protein disulfide bonds by the enzyme thioredoxin?

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11ecba2d_0e90_adfa_a3bf_fbd965166496_MD0008_00 Oxidation is the loss of electrons that occurs when an electron donor transfers electrons to an acceptor. The reverse process, referred to as a reduction, involves the gain of electrons. In general, reactions in which an acceptor becomes reduced and a donor becomes oxidized are called oxidation-reduction, or redox, reactions. Enzymes that catalyze redox reactions are collectively known as oxidoreductases. In proteins, disulfide bonds form when the thiol groups of cysteine residues are oxidized, linking them together to form cystine. To break the disulfide bond in cystine, a reduction step that transfers electrons back to the sulfur atoms is required. Thioredoxin catalyzes the transfer of electrons from a donor molecule to cystine, which reduces the sulfur atoms and oxidizes the donor molecule. Consequently, thioredoxin can be classified as an oxidoreductase because it facilitates the cleavage (reduction) of disulfide bonds. (Choice A) Proteases are a type of hydrolase that break peptide bonds by hydrolysis (addition of water). They do not break disulfide bonds. (Choice B) Isomerases rearrange functional groups within a molecule but do not catalyze redox reactions. Therefore, they cannot catalyze cleavage of disulfide bonds. (Choice C) Phosphorylases are a type of transferase that break bonds by adding phosphate, as in glycogen degradation. They do not catalyze redox reactions and cannot break disulfide bonds. Educational objective: Disulfide bonds form in proteins when two cysteine residues are oxidized (lose electrons) to form cystine. They must be reduced (gain electrons) for the bond to break. Enzymes that catalyze oxidation-reduction reactions (transfer of electrons) are collectively known as oxidoreductases.

Which Statement Correctly Describes the Cleavage of Protein Disulfide Bonds