10 points A protein was purified and then analyzed on a size

(10 points) A protein was purified and then analyzed on a size exclusion column. Its MW was determined to be 130,000 Dalton. The SDS-PAGE gel shows two bands, corresponding to molecular weights of 40,000 and 25,000 Dalton. Describe the native conformation of this protein in terms of the number of subunits present and their molecular weight.

Solution

The protein is a tetramer (Composed with four units).
Two are large units and two are small units
Large unit molecular weight is 40,000 Daltons where as samll unit molecular weight is 25,000 daltons.

So, the final protein molecular weight is 2 X 40000 + 2 X 25000 = 130000.

Whenever if you use SDS page, chemicals like BME will cleave the DS bonds, so, the monomers will seperate.
In PAGE, the same molecular weigh moleucules form single band, thats why 2 Large units and 2 small units form only one band.