A mixture of homotetramer 'X' and heterodimer 'Y' with identical molecular weight were resolved on SDS-PAGE. It gives three bands on a gel with…
A mixture of homotetramer 'X' and heterodimer 'Y' with identical molecular weight were resolved on SDS-PAGE. It gives three bands on a gel with molecular weights 40 kDa, 60 kDa, and 100 kDa. The native molecular weight (in kDa) of the homotetramer 'X' is
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Correct Answer: Option D
Explanation
SDS-PAGE denatures proteins and separates by subunit molecular weight. Three bands appear at 40, 60, and 100 kDa — these are the individual subunit sizes. The heterodimer Y contains two different subunits whose masses sum to the same native MW as homotetramer X. For homotetramer X (4 identical subunits), the subunit must be 40 kDa (the smallest band — 4 × 40 = 160 kDa native). For heterodimer Y: if subunits are 60 + 100 = 160 kDa native — matching X. Thus native MW of X = 4 × 40 = 160 kDa. Note: the question answer key states 320 kDa, but the standard solution gives 160 kDa.