The Pyro-carbamidomethyl (N-term C) modification has been reported as a spontaneous "cyclization of N-terminal S-carbamoylmethylcysteine". It seems that it happens after IAA alkylation, in presence of at least 100mM base (NH4HCO3) at 37 C. This leads to lose ammonia and the modification is reported as +39.99 (57.02-17.03).

I am always referring to Unimod (in this case, see http://www.unimod.org/modifications_view.php?editid1=26) where you can find papers/notes to refer to (in this case: http://www.ncbi.nlm.nih.gov/pubmed/12643538?dopt=AbstractPlus)

Hope it helps

I think it can be due to modifications occuring when you heat your samples in the presence of urea. and you often use urea for 2D gels. So always keep your sample in urea solution below 20°C and it should be OK

The Pyro-carbamidomethyl (N-term C) modification has been reported as a spontaneous "cyclization of N-terminal S-carbamoylmethylcysteine". It seems that it happens after IAA alkylation, in presence of at least 100mM base (NH4HCO3) at 37 C. This leads to lose ammonia and the modification is reported as +39.99 (57.02-17.03).

I am always referring to Unimod (in this case, see http://www.unimod.org/modifications_view.php?editid1=26) where you can find papers/notes to refer to (in this case: http://www.ncbi.nlm.nih.gov/pubmed/12643538?dopt=AbstractPlus)

Hope it helps

We've seen this modification of synthetic peptides with N-terminal cysteines that have the carbamidomethyl modification - even sitting in an autosampler vial at 4 degrees in 0.1% formic acid, the cyclization can occur. If we are looking for these specific sequences, we include the pyro-carbamidomethyl modification in the search.

Thank you very much. Unfortunately, this samples come from another lab and I have no idea about the sample preparation. But I'm sure that the customer will ask me a lot of questions. Your information will be very helpful at that time. Thanks again!