Probably Molecular Biology 101, but I was wondering if anyone could tell me how an amino acid's pKa can be altered by protein environments and also by surrounding charge?

 

e.g. Glutatate and aspartate can hold onto protons around the physiological pH in some instances (microenvironment and surrounding charge) when their pKa is much lower - how do they do this!

Probably Molecular Biology 101, but I was wondering if anyone could tell me how an amino acid's pKa can be altered by protein environments and also by surrounding charge?

 

e.g. Glutatate and aspartate can hold onto protons around the physiological pH in some instances (microenvironment and surrounding charge) when their pKa is much lower - how do they do this!

 

It has to do with the situation. If hydrogen bonding networks established are unable to be interrupted then the proton will remain attached to the amino acid.

 

Protein shape can also have an effect. If the shape is such that it shields the side chains from outside effects, then the proton will be unable to leave.