Search

This study reports the transformation of nitrogen during liquefaction of two microalgae (i.e., Chlorella vulgarisand Spirulina) in subcritical/supercritical ethanol at 220–260 °C. The nitrogen contents in all products from microalgae liquefaction were quantified, and the nitrogen species in those products were characterized. The nitrogen in the raw microalgae are mainly present in the form of protein-N, with a small fraction of nitrogen present in other forms such as quaternary-N, inorganic-N, and pyridinic-N/amine-N. The nitrogen in the solid residue is found to decrease significantly at 220 °C. As the liquefaction temperature further increases, the nitrogen in char gradually decreases, accompanied by the increase of nitrogen in bio-oil, i.e., up to 83.2% at 260 °C for Chlorella vulgarisand 90.1% at 250 °C for Spirulina. The results demonstrate that the nitrogen species in the raw microalgae are not stable and easily transformed into other N-containing species in bio-oil (mainly the pyrrole and amine species). A small fraction of pyrrolic-N is also formed in the solid residue at 220 °C, while the formation of N-containing gas species is negligible.

Glycosylation is one of the most important post-translational modifications in biological systems. Current glycoproteome methods mainly focus on qualitative identification of glycosylation sites or intact glycopeptides. However, the systematic quantitation of glycoproteins has remained largely unexplored. Here, we developed a chemoenzymatic method to quantitatively investigate N-glycoproteome based on the N-glycan types. Taking advantage of the specificity of different endoglycosidases and isotope dimethyl labeling, six N-glycan types of structures linked on each glycopeptide, including high-mannose/hybrid, biantennary, and triantennary with/without core fucose, were quantified. As a proof of principle, the glycoproteomic N-glycan type quantitative (glyco-TQ) method was first used to determine the N-glycan type composition of the immunoglobulin G1 (IgG1) Fc fragment. Then we applied the method to analyze the glycan type profile of proteins from the breast cancer cell line MCF7, and we quantitatively revealed the N-glycan type microheterogeneity at the glycopeptide and glycoprotein level. The novel quantitative strategy to evaluate the relative intensity of the six states of N-glycan type glycosylation on each site provides a new avenue to investigate the function of glycoproteins in broad areas, such as cancer biomarker research, pharmaceuticals characterization, and antiglycan vaccine development.