5+ Year Member
- Aug 29, 2012
- Medical Student
Histidine's side chain has a pKa of 6.05... doesnt that make it an acidic side chain? Why is it considered basic?
Good question. I had to brush off the dust on my Biochem book for this one. It sounds like the two nitrogens that are part of the imidazole ring on histidine's side chain give the amino acid both acidic and basic properties. The basic nitrogen (with the free electrons) can abstract a proton from a donor group, only to have it shuttled and relayed to another group via its more acidic nitrogen.Histidine's side chain has a pKa of 6.05... doesnt that make it an acidic side chain? Why is it considered basic?
Yeah, for the most part. Some small fraction will still remain protonated (remember the Henderson-Hasselbach equation), but you should think of histidine as being basic under physiologic conditions.thanks for that explanation! So we should still think of it as deprotonated at pH's past 6.05?