[AMBER] Histidine tautomer state and pKa?

From: Liao via AMBER <amber.ambermd.org>
Date: Sat, 3 Sep 2022 21:53:15 -0400

Dear List,

From what I read and know, for histidine, the HIE tautomer is the more common one on proteins, that the N3 nitrogen is the one protonated. But surprisingly, the pKa for the N3 is also lower, about 0.5 units less than N1, HID. Why is this the case? The lower pKa one should be the one that’s deprotonated, not the other way round. This seems quite puzzling to me. Any help will be appreciated, thanks.

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Received on Sat Sep 03 2022 - 19:00:02 PDT
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