BL/CH 401 Lecture #3 - Acids, Bases, and Buffers

7. Calculating pI (Isoelectric Point or pH) of His:

Here is how to calculate the pI (for His in this example and for all other complex amino acids too):

After you find the His form with no net charge, then take the pK going toward the His+1 form as the lower pK,

Next find the pK going toward the His-1 form as the upper pK, and finally average these two pKs to get pI.

The calculation for the pI of His is shown below:

So for any amino acid, fing the AA 0 form (ie. form with no net charge), then average pK going to AA+1

with the pK going to AA-1, to get pI.

Try to calculate the pI of another of the 5 complex amino acids or even all of them!

©Wilbur H. Campbell, 1995, 1996; wcampbel@mtu.edu

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