Viral Neuraminidase - Exo- and Endo-

Exo- and Endo-

Neuraminidase enzymes can have endo- or exo-glycosidase activity, and are classified as EC 3.2.1.29 (endo-neuraminidase) and EC 3.2.1.18 (exo-neuraminidases). In general, mammalian sialic acid residues are at terminal positions (non-reducing end) in complex glycans, and so viral neuraminidases - which are exo-glycosidase enzymes - use these terminal residues as their substrates.