Of especial note is the transformation of maltose by maltase into glucose, and of cane sugar by invertase into a mixture of glucose and fructose (invert sugar); other instances are: lactose by lactase into galactose and glucose; trehalose by trehalase into glucose; melibiose by melibiase into galactose and glucose; and of melizitose by melizitase into touranose and glucose, touranose yielding glucose also when acted upon by the enzyme touranase.
Lastly, when d-galactonic acid is heated with pyridine, it is converted into talonic acid, which is reducible to talose, an isomeride bearing to galactose the same relation that mannose bears to glucose.
Of the ketoses, we notice d-sorbose, found in the berries of mountain-ash, and d-tagatose, obtained by Lobry de Bruyn and van Ekenstein on treating galactose with dilute alkalis, talose and l-sorbose being formed at the same time.
Boletus edulis, in the Oriental Trehala and in ergot of rye; melibiose, C12H22011, formed, with fructose, on hydrolysing the trisaccharose melitose (or raffinose), C18H32016.5H20, which occurs in Australian manna and in the molasses of sugar manufacture; touranose, C12H22011, formed with d-glucose and galactose on hydrolysing another trisaccharose, melizitose, C,8H32016 2H20, which occurs in Pinus larix and in Persian manna; and agavose, C12H22011, found in the stalks of Agave americana.
On reducing the lactone prepared from the inactive acid an inactive galactose is obtained from which l-galactose may be separated by fermentation.