Determine the subunit composition of a protein from the foll

Determine the subunit composition of a protein from the following information:

Molecular mass by gel filtration: 250 kDa

Molecular mass by SDS-PAGE (without BME): 55 kDa, 50 kDa, 45 kDa

Molecular mass by SDS-PAGE (with BME): 50 kDa, 45 kDa, 30 kDa, 25 kDa

Solution

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  Gel filtration :

it does not affect the interaction between the various subunits in your protein.
Thus, protein appears to be 250 kDa in size.
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SDS-PAGE :

Molecular mass by SDS-PAGE (without BME): 55 kDa, 50 kDa, 45 kDa

It involves boiling the samples, and running them under denaturing conditions.

It will disrupt the association between the two 100 kDa subunits.

he protein contains two 100-kD polypeptides and two 50-kD polypeptides.

Each 50-kD chain is disulfide bonded to a 100-kD chain. T

the 100-kD units associate noncovalent bond and gives 55kDa and 45 kDa.

Molecular mass by SDS (wBME):50kDa,45kDa,30kDa,25kDa

BME is a reducing agent .

it reduces the disulfide bonds in proteins.

In other words the R1-S-S-R2 bond between the 50 and 100 kDa fragments.

They is reduced to R1-SH and R2-SH, two separate proteins.

Together with the SDS page that fully denatures and separates all the subunits of protein.