A protein sample isolated from natural source was electrophoresed on a non-reducing SDS-PAGE. It migrated as a band corresponding to 60 kDa. When…
A protein sample isolated from natural source was electrophoresed on a non-reducing SDS-PAGE. It migrated as a band corresponding to 60 kDa. When the same protein was electrophoresed on a native-PAGE its migration corresponded to a 120 kDa marker protein. What is a reasonable inference?
Select an option to attempt
Correct Answer: Option C
Explanation
SDS-PAGE and native-PAGE interpretation:Observations:• Non-reducing SDS-PAGE: single band at 60 kDa — SDS denatures protein and separates subunits; all subunits are 60 kDa, non-reducing conditions leave disulfides intact but SDS disrupts non-covalent interactions.• Native-PAGE: migration corresponds to 120 kDa protein — under native conditions, the protein's quaternary structure is preserved.Conclusion: The protein is a DIMER of two 60 kDa subunits (120 kDa total), held together by NON-COVALENT interactions (not disulfides), because:• Non-reducing SDS still gives 60 kDa (if disulfides held the dimer, non-reducing SDS would give 120 kDa).• If it were disulfide-linked, non-reducing SDS-PAGE would show 120 kDa.Answer: The protein is a dimer of 60 kDa subunits that are NOT linked by disulfides (Option 1).