The first step in a crude ovalbumin purification protocol is

The first step in a crude ovalbumin purification protocol is the addition of ammonium sulphate, the subsequent step is the addition of sulphuric acid, what are the roles of these reagents in a protein purification procedure?

Solution

ammonium sulphate decreases solubility of protien in solution in a procedure called salting out( because the water molecules that were interacting with hydrophillic protien residues interact with salt now ) , on increasing ammonium sulphate as the solubility of dissolved protien tends to decrease, the seperated protien molecules tend to aggregate together and eventually precipitate down.

in a solution pH that is lower than pI, surface of the protein is mostly positively charged and repulsion between proteins tends to occurs. However, at isoelectric point pi the - and + charges tend to cancel, thus repulsive electrostatic forces are reduced and the attraction forces mostly win . The attraction forces will causes protiens to aggregation and precipitation a bit faster. The pI of most proteins is in the pH range of 4–6. that is why acids like hydrochloric and sulfuric acid are used to aid in precipitation.

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