... mixtures, a dramatic advantage of the top-down approach isthat a final separation stage can be done in the FT MS instrument. For example, after rough separa-tion of the proteins from Arabidopsis thaliana, ... covalent modifications of the enzyme, the effect of the inhibitor on the molecular mass value of HAD was measured; instead of an adduct increase, orno change, the value had unexpectedly decreased from22 ... 4 Da, the decrease of the molecular mass value. The most proba-ble reason for a 2 Da decrease is the formation of anS–S bond; although this was totally unexpected andunprecedented, the top-down...