What is the overall charge of the Pro-Met-Phe-Ser-Glu-Leu polypeptide at pH #7.2#? I've drawn it, and I think it's #-1#, but I'm not 100% sure.

1 Answer
Truong-Son N.
Sep 22, 2015

I recently got my homework graded and returned, and yep, it's a #-1# charge.

The polypeptide looks like this:

The glutamate sidechain has a pKa of #4.07#, making its basic/deprotonated form more dominant at pH #7.2#.

The N-terminus and C-terminus have pKas of #~8.0# and #~3.1#, respectively. Therefore, the N-terminus must be acidic/protonated, and the C-terminus must be basic/deprotonated.

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