Since some amino acids, such as Glu and His, can be viewed as weak acids or bases, the ratio of their protonated form to their deprotonated form is dependent on pH. Furthermore, you can use this knowledge to predict whether a given amino acid will exist predominantly in its protonated or deprotonated form at a given pH. To do this, it is easier to think about the pK, of the amino acid functional group. Recall from general chemistry that the pK, is equal to -log(K). Using the K, value for the Glu side chain, which is 5.62 x 10-5, calculate the pK, for the Glu side chain. pKa =