Chapter 16 - Mass Tags and Isotope Tags

Abstract

This chapter explores a method of analyzing protein samples, and also discusses major mass tag types and general protocols for their use. Mass tags are modification reagents that contain a reactive group for coupling to biomolecules and another component of known mass, which behaves predictably upon MS separation. MS analysis of mass tagged peptides can be done by focusing only on those peptides that contain an additional mass component representing the tag's known mass contribution. Thus, all other peaks on the MS spectrum can be ignored, which greatly reduces the complexity of the sample. Mass tag reagents have been developed with reactive groups to modify specifically only certain low frequency amino acids within proteins. The design of mass tags can be combined with stable isotope labels to create more than one mass unit for each tag type. It can be broad spectrum in its modification properties to derivatize all peptides as they are formed upon proteolysis. Other broad-spectrum mass tag modification agents are designed to modify all amine groups and yield tags on every peptide at their N-terminal amines. The different forms of mass tags are ICAT reagents, ECAT reagents, and isobaric tags.