We have cysteine, and we have lysine. Now, for the case of cysteine, the side chain group that is ionizable is the following group. So notice the sulfur atom contains an h atom. But when the PH value reaches the PKA value of the side chain group, namely 8.3, what that means is this will begin to lose our h atom. And at the PH value of 8.3, exactly half of the cysteine amino acids will exist in this form, and the other half will exist in this form with a negative charge on that sulfur. Now, if we go above 8.3, then this group will predominate.