Why is Histidine positively charged at pH 7 ?
Why is Histidine positively charged at pH 7 when the side chain has a pKa of 6?
Oh no, you are correct, it should not be positive in physiological conditions. Histidine is a zwitterion at ph7. In acidic environments however, it does become positively charged. Just be careful when they ask you questions about the over all charge of a protein, keep in mind the environmental pH.
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