Sialidases are widely distributed in nature, from microorganisms to mammals. Mammalian sialidases differ in their tissue distribution, subcellular localization, substrate specificity and pH optimum. To date, several mammalian sialidases have been cloned; a lysosomal form (Neu1), a cytosolic form (Neu2), a plasma membrane-associated form (Neu3) and a lysosomal/mitochondrial form (Neu4). Defining th ...