Question

Biochemistry: If a protein has a pI of 7, what pH should the buffer in the S column be to ensure that the protein binds to the resin?

Answer 1

pI: Isoelectric point: This is the pH at which the amino acid is electrically neutral overall or exists in what is known as Zwitter ion form.

For the protein to reliably bind to a resin column, it should be charged and not neutral. To make a particular protein charged, we need to adjust the pH of our buffer such that it allows either the amino or carboxyl group in the amino acid part to exist as ion but not both else it would be neutral.

From various studies, it has been found that a pH that is atleast ONE unit away from the pI of the protein that we are isolating or purifying is ideal to make sure that the protein binds to the resin.

Since our protein has a pI>6.94, it is a basic protein(Criteria for basic protein classification).

Once we know this, it has further been found that if we keep the pH of buffer to 1 unit below the pI, the efficiency of purification is better comapared to when pH is 1 unit more than pI.

Thus, the pH of our buffer should be less than 6.

Answer: pH 6.