To detect the deamidation from Glutamine to Glutamate in a protein, normal practise seems to be a mass spec, where it is claimed there is a change of 1 dalton.
EG It is claimed that:
Deamidation of an Asn to Asp/IsoAsp results in an increase in mass of a single dalton.
But when I look at their table, they are using Glutamic Acid as being 1 Dalton heavier than Glutamate, but at pH 7 the Glutamic Acid will be deprotonated to Glutamate. Do they put the sample in pH 4 to protonate the Glutamate first? But then you are risking catalysing the hydrolysis of Glutamine anyway, rendering your results useless!
There should be a charge difference though, as you are going from neutral to a negative charge, so that would show up in a change in mass/charge on the mass spec, rather than a mass change.
Any help would be appreciated.