Charged Amino Acids
Negatively charged Positively charged
It is false to presume that Histidine is always
protonated at
typical pHs. The side chain has a pKa of
approximately 6.5,
which means that only about 10% of of the species
will be
protonated. Of course, the precise pKa of an amino
acid depends
on the local environment.
Partial positive charge