What was I talking about? New cysteine labeling approaches! There are lots of reasons to want to label your cysteines instead of your lysines and arginines. Maybe your search engine can't handle 2 modifications per lysine. Maybe just about every post-translational modification (PTM) appears to happen...on lysine....maybe you're just interested in cysteine peptides in general (at least a few sensor proteins in humans (Nrf?) rely on the state of a cysteine within its own structure as a stress detection mechanism.)
So in this new....wait...this is from last April. Why did I read a 1 year old paper? Because someone on Twitter pointed it out. And you can get great info from even ancient research from 2015. Wow. This post is spastic.
In this study from Liqing Gu et al., out of the University of Pittsburgh, this team shows you how to quantitatively study cysteines using 2 extremely thorough methodologies. How thorough?
They do all this work on an Orbitrap Velos. In case you aren't impressed by the experimental design, they also employ gas phase fractionation on the Velos and describe the increase in coverage they get from that approach -- following SCX fractionation.
From the 2 approaches above, they find highly complementary results when looking at mouse liver proteomes. Is it overkill? Possibly. But that isn't the point here. I like this paper because its an extremely different direction. If it looks like you need to be paying more attention quantitatively to what is happening to the cysteines in your organism (or if you just want to try something new with that system that is driving you insane) this is a comprehensive resource on the topic.