https://www.selleckchem.com/products/l-dehydroascorbic-acid.html Protein-specific glycoform analysis is essential for the thorough understanding of cellular chemistry and signaling but presents a significant assay challenge for small-sized, free-floating exosomes, ubiquitous regulators of cellular physiological functions and mediators of intercellular communication. We report herein a quantitative localized analysis (QLA) method for the first-time achievement of a protein-specific glycosignature assay on these important extracellular vesicles. The integration of localized chemical remodeling and quantitative electrochemistry allows the proof-of-concept QLA examination of exosomal mucin 1 (MUC1)-specific terminal galactose/N-acetylgalactosamine (Gal/GalNAc). In combination with sialic acid (Sia) cleavage manipulation for the exposure of originally capped Gal/GalNAc, QLA has revealed distinct MUC1-specific sialylation capping ratios for MCF-7 and MDA-MB-231 exosomes, as well as when compared to parent cells. These findings suggest a useful noninvasive indicator for subtyping cancer cells and exosome secretion as a likely venue for the preservation of cellular compositional and functional integrity. The QLA method also permits dynamic monitoring of changes in the exosomal MUC1-specific sialylation capping ratio, enabling the distinction of biogenesis pathways of exosomes.Thermal and other transport coefficients were recently shown to be largely independent of the microscopic representation of the energy (current) densities or, more generally, of the relevant conserved densities/currents. In this Article, we show how this gauge invariance, which is intimately related to the intrinsic indeterminacy of the energy of individual atoms in interacting systems, can be exploited to optimize the statistical properties of the current time series from which the transport coefficients are evaluated. To this end, we introduce and exploit a variational principle that relies on the me