Q. 36 Among the reagents given below which one of the combination of reagents will NOT break the
disulphide bonds in the immunoglobulin molecules?
(P) Reduced glutathione
(Q) Dithiothritol
(R) Sodium dodecyl sulphate
(S) Methionine
(A) R&S
(B) 𝑃&𝑅
(C) P& S
(D) Q&R
Disulfide bonds stabilize immunoglobulin structures, and specific reducing agents target these bonds. The correct answer is (A) R&S, as sodium dodecyl sulphate (SDS) and methionine fail to cleave them.
Correct Answer
The combination that will NOT break disulfide bonds in immunoglobulin molecules is R (Sodium dodecyl sulphate) and S (Methionine). Option (A) R&S is correct.
Option Breakdown
Immunoglobulins rely on disulfide bonds between cysteine residues for structural integrity. Reducing agents with free thiols perform nucleophilic attacks to cleave these bonds.
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P: Reduced glutathione breaks disulfide bonds via its thiol group, acting as a reductant in protein refolding and antibody processing.
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Q: Dithiothreitol (DTT) effectively reduces disulfide bonds, commonly used in biochemistry due to its strong reducing power and stability.
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R: Sodium dodecyl sulphate (SDS) denatures proteins by disrupting hydrophobic interactions and hydrogen bonds but lacks a thiol group to reduce covalent disulfide bonds.
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S: Methionine serves as a sulfur-containing amino acid that does not function as a reducing agent for disulfide bonds; it cannot perform the required thiol-disulfide exchange.
Why R&S Fail
SDS aids electrophoresis by linearizing proteins without cleaving disulfides, requiring separate reductants like DTT or beta-mercaptoethanol. Methionine, lacking a free thiol in its standard form, shows no reducing activity toward S-S bonds in proteins like immunoglobulins.
