Question

BIOCHEM LAB: Why did you carry out dialysis of your protein sample after the addition of ammonium sulfate on day 2 of the purification? Did your protein sample volume increase? Explain why or why not.

Answer 1

i) After precipitating the protein fraction with ammonium sulphate, it is essential to remove the ammonium sulphate before proceeding to the subsequent purification process. One of the simplest methods to remove the ammonium sulphate is by dialysis of the solution.

ii) Dialysis of the precipitated protein solution will increase the volume. This is because of the initial osmotic effect of the ammonium sulphate and to prevent the membrane tube from bursting because of the increased volume, an air gap at the top of the membrane tube is usually made