Many glycoproteins are present in both gram-positive and gram-negative bacteria. Glycans are typically found in surface proteins, such as flagella and pili. Some well-studied organisms with O- and N-glycosylation are Neisseria gonorrhoeae, Pseudomonas aeruginosa, and Campylobacter jejuni. Although there seems to be a common evolutionary origin, their biosynthetic pathways differ from eukaryotes. Therefore endoglycosidases such as PNGaseF, Endo H, or O-glycosidase, do not recognize their sugars and cannot be used to analyze these samples. Depending on the nature of the glycan, exoglycosidases can be active on bacterial carbohydrates, as long as the individual residues are not modified by methyl, acetyl, and other groups commonly found in prokaryotic sugars.