So in your textbook, or maybe your teacher might give you different PKA values. And that's because the temperature conditions or other conditions under which that amino acid exists in are different. So let's move on to the second case. If the side chain is ionizable and that ionizable side chain is acidic, then to find a pi value of that amino acid, we simply take the average of the PKA values of the terminal alpha carboxyl group and that side chain. So to see what we mean, let's take an example. Let's look at an ionized blamino acid that is acidic.