Occurrence of free glycans in salmonid serum.

Free N-glycans (FNGs) are oligosaccharides that are structurally related to N-linked glycans, and are widely found in nature. The mechanisms responsible for the formation and degradation of intracellular FNGs are well characterized in mammalian cells. More recent analysis in mammalian sera shows that there are various types of extracellular free glycans, including FNGs. However, it is unknown whether these free glycans are widely distributed in vertebrates. In this study, we investigated the occurrence of free glycans in salmonid serum. We found that it contained sialyl or neutral FNGs and sialyl lactose/N-acetyllactosamine (LacNAc)-type glycans, which was consistent with that found in mammalian sera. Many of the structures of FNGs matched those of N-glycans from serum glycoproteins. This study revealed that various types of free glycans are present in fish serum, demonstrating their wide occurrence among vertebrates.