Question

Consider the following proteins: human serum albumin (pI of 4.7 and a MW of 66,463 Da) and lysozyme (pI of 11.35 an MW of 14,307 Da) To which of the following will human serum albumin bind? To which of the following will lysozyme bind? Choose all correct answers.

a. anion exchange column 3.5

b. anion exchange column 7.5

c. anion exchange column 10.1

d. cation exchange column 3.5

e. cation exchange column 7.5

f. cation exchange column 10.1

please fully explain your answer.

Answer 1

The protein binding to the ion excahge column depend on the pI of protein. Human serum albumin has a pI of 4.7, which means that in acidic pH (pH less than 4.7 ) the protein will be protonated and it will be positively charged (cation) and hence it bind to cation exchange column at pH less the 4.7. At pH larger than pI (pH more than 4.7), the protein will get deprotonated and it will be negatively charged (anion) and it will bind to anion exchange column at pH larger than 4.7.

So Human serum albumin will bind to (b) anion exchange column 7.5, (c) anion exchange column 10.1, and (d) cation exchange column 3.5.

The pI of lysozyme is 11.35, so at pH less than 11.35, it will be protonated and positively charged (cation) so it will bind to cation exchange coloum at pH less than 11.35.

So lysozyme  will bind to (d) cation exchange column 3.5, (e) cation exchange column 7.5 and (f) cation exchange column 10.1.