<unk> s are a family of enzymes that catalyse the degradation of<unk> uronic acid (HA). Karl Meyer classified these enzymes in 1971, into three distinct groups, a scheme based on the enzyme reaction products. The three main types of<unk> s are two classes of eukaryotic endoglycosidase hydrolases and a prokaryotic lyase-type of glycosidase. In humans, there are five functional<unk> s:<unk> 1,<unk> 2,<unk> 3,<unk> 4 and<unk> 5 (also known as SPAM1 or PH-20); plus a pseudogene,<unk> 6 (also known as<unk> P1). The genes for<unk> 1-3 are clustered in chromosome 3, while<unk> 4-6 are clustered in chromosome 7.<unk> 1 and<unk> 2 are the major<unk> s in most tissues. GPI-anchored<unk> 2 is responsible for cleaving high-molecular weight HA, which is mostly bound to the CD44 receptor. The resulting HA fragments of variable size are then further hydrolized by<unk> 1 after being internalized into endo-lysosomes; this generates HA oligosaccharides. According to their enzymatic mechanism,<unk> s are<unk> uronoglucosidases (), i.e. they cleave the (1->4)-linkages between N-acetylglucosamine and glucuronate. The term<unk>  may also refer to<unk> uronoglucuronidases (), which cleave (1->3)-linkages. In addition, bacterial<unk> uronate lyases () may also be referred to as<unk> s, although this is uncommon.
Hyaluronidase
Iduronidase
Pegaspargase
Lactase
Presepsin
Imlifidase
Amidase
Glucuronosyltransferase