Abstract: The present invention relates to methods allowing the selective enrichment of N-terminal fragments of polypeptides and/or peptides from complex samples by combining a particular polypeptide/peptide labeling and fractionation strategy with specific chemical and/or enzymatic reactions targeting the N-terminal fragments to be analyzed.

Abstract: The present invention relates to kits and methods for the isotopic/isobaric labeling and the subsequent affinity selection and analysis of proteinaceous molecules. In particular, the invention relates to a kit-of-parts comprising a combinatorial plurality of labeling reagent for the labeling of proteinaceous molecules, each labeling reagent comprising an isobaric label component, an isotopic label component, and a reactive group capable of reacting with a proteinaceous molecule, wherein the isotopic label component concomitantly is an affinity tag. The invention is also directed to a corresponding method for the analysis of proteinaceous molecules, comprising labeling at least one subset of the proteinaceous molecules present by employing a kit-of-parts as defined herein and subsequently separating the labeled molecules by affinity purification via the affinity tag comprised in the label. Finally, the invention relates to the uses of such methods for protein expression profiling or proteomic analyses.

Abstract: The present invention relates to the selective enrichment of post-translationally modified proteins and/or peptides from complex samples, wherein the post-translational modification is glycosylation, by combining a particular protein/peptide labeling protocol with the specific selection of the post-translationally modified proteins and/or peptides to be analyzed.

Abstract: Subject of the present invention are new isotopic and isobaric tagged molecules, kits comprising them and methods of using them in mass spectrometry.