Biology Stack Exchange is a question and answer site for biology researchers, academics, and students. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

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.

share|improve this question
This might be better on chemistry SE. – dd3 Jul 22 '13 at 21:07
Its more relevant to Biology as its to do with Proteins I think. – Nick Jul 22 '13 at 21:30
I am not an expert in this area but this is what I understand. Usually ESI based protein mass spec imparts a positive charge on the proteins by protonation. Formic acid is usually added to help in protonation. In deamidation -NH2 is replaced by -OH thereby increasing the mass by 1 dalton (14+2 -> 16+1). I think that glutamine may be also acquire multiple charge (by NH2 protonation). You can see this article, which talks about dealing with deamidation artifacts resulting from sample preparation techniques. – WYSIWYG Jul 22 '13 at 21:46
Ah, so the samples are put in acidic conditions to protonate the glutamate which can result in false positives, interesting. – Nick Jul 23 '13 at 7:10
Biochemistry is still chemistry :) – MattDMo Jul 23 '13 at 16:04

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Browse other questions tagged or ask your own question.