Biotinylation Option for Cysteine Missing

Issue

Proteome Discoverer 2.2 user was modifying settings in the Sequest HT node, and he wanted to add biotinylation on Cysteine as a dynamic modification (see image below), but the option was not available, even after going into the Maintain Chemical Modifications section in Administration and making sure that it was available there.

Environment

• Mass Spectrometry
• Proteome Discoverer 2.2

Resolution

It turned out that Cysteine was already occupied in section 7, the static modification section (carbomidomethyl modification). Once this static modification is removed, it frees up Cysteine to be available for biotinylation.