Question

If you have 4 Lysines, the side chain of Lysine has a Pka value of around 11, you are at pH of 4, are you going to take a proton off or to add? What is the net charge of these four Lys? What kind of ion exchange chormatography would you use?

Answer 1

First lets understand what is pH,PI and Pka value

pH is the measure of of concentration of H⁺ in a solution or its the negative logarithm of the molar concentration of H⁺ ion

Lower pH = more H⁺  ion more acidic

Higher pH = Less H⁺ ion less acidic

Pka is association constant. It's the negative logarithm of the ratio of dissociated acid and conjugated base

pI also called as isoelectric point It's the pH at which charge on molecule is zero

Given in the question  4 Lysines, the side chain of Lysine has a Pka value of around 11, at pH of 4, are we going to take a proton off or to add and  What is the net charge of these four Lys

To calculate charge on lysine we have to calculate pI of lysine from Pka

As the Total Net charge is Positive +4 we will use Cation exchange chromatography