A mixture of leucine, histidine, and aspartic acid is put in an electrophoresis apparatus in a buffer at pH=6.0. ?

Question

Which of the amino acids will travel toward the positive electrode when voltage is applied?

A) leucine

B) histidine

C) aspartic acid

Answer 1

To answer this, you need to look at the structure of each amino acid along with the respective pKa values and/or the pI.

Looking up pI values, I find the following:

leucine pI = 5.98, so at pH 6 it will be neutral

histidine pI = 7.59, so at pH 6 it will have a net positive (+) charge

aspartic acid pI = 2.77, so at pH 6 it will have a net negative (-) charge

Thus, aspartic acid would migrate toward the positive electrode as it is negatively charged.