Also known as hyaluronic acid, hyaluronate. It is the simplest glycosaminoglycans and unusual because: 1) it does not contain sulphated sugars, or complex arrangements of a number of different disaccharide units, 2) it has the longest chain (around 25,000 non-sulphated disaccharide units), 3) it is not covalently linked to other proteins to make proteoglycans, 4) and it is not made in the cell and released by exocytosis, but instead it is made by an enzyme complex at the cell surface. A small amount of hyaluronan absorbs and swells up a large volume, so this glycosaminoglycans is a useful space-filler.