CHEN 3701 Lecture Notes - Lecture 11: Acid Dissociation Constant, Protonation
8 Oct 2015
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Example: an enzyme has the following sequence in the region that interacts with the substrate ahgks (polypeptide). It is more active in the cytosol (ph ~ 7) than the lysosome (ph 4-5). What does ahgks look like? pka = 6, histidine (h) N terminus lysine (k) pka = 10. 5 c terminus. It is most optimal in its protonated form in lysosome, ph is smaller than both pkas, so both sites will be protonated just want the lysine part protonated this is optimal form with lysine being protonated. It is detrimental to deprotonate the lysine and it is also detrimental to protanate the histidine: rate, [ehs] pssa, material balance. Into pssa (2) plug this into rate eqn can find optimal proton concentration by setting derivative of rate equal to 0 d = deprotonated p = protonated this enzyme is most active at ph 8. 3.
