[HughMyron]

Specifically, the question asks:

A 1:1 mixture of phenylalanine and proline was analyzed by electrophoresis at pH 7.  What happens?

Phenylalanine has pKa's of 2.16 and 9.18. Its isoelectric point is pI = 5.67.

Proline has pKa's of 1.99 and 10.60. Its isoelectric point is pI = 6.30.

So, at pH = 7, we have pH > pI, meaning that both amino acids are negative. So both of them will move towards the positive electrode, right?

My questions are:
1) Was what I said correct? and
2) Phenylalanine is expected to move faster because its pI is lower, right?

[Babcock_Hall]

I believe that you are correct.  The chemistry of the stacking gel versus the resolving gel in SDS PAGE is a practical appliction of how pI and pH affect the mobility of glycine.

[hunypowell]

glad I came across this one. Thanks so much!