Q.18 2-mercaptoethanol breaks the ________ covalent bond between light and heavy
chains of an immunoglobulin molecule.
(A) C-N
(B) N-O
(C) S-C
(D) S-S
2-Mercaptoethanol Breaks S-S Covalent Bond in Immunoglobulin Chains
2-Mercaptoethanol (2-ME), a reducing agent, specifically targets disulfide bonds in proteins like immunoglobulins. The correct answer to the question is (D) S-S, as it cleaves the disulfide bridges linking light and heavy chains.
Correct Answer
(D) S-S
Immunoglobulins (Ig), or antibodies, feature light chains (L) and heavy chains (H) connected by disulfide bonds (S-S), formed between cysteine residues’ thiol groups (-SH). 2-Mercaptoethanol reduces these S-S bonds to two -SH groups, dissociating H and L chains without affecting peptide backbones.
Option Explanations
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(A) C-N: Incorrect. C-N bonds form the peptide backbone; 2-ME does not hydrolyze them, as it lacks protease activity.
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(B) N-O: Incorrect. N-O bonds rarely occur in proteins; no evidence links 2-ME to their cleavage in immunoglobulins.
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(C) S-C: Incorrect. S-C bonds exist in methionine but are stable to 2-ME, which targets only S-S linkages selectively.
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(D) S-S: Correct. Studies confirm 2-ME preferentially reduces interchain S-S bonds between L and H chains at low concentrations.
