Aliphatic (R)-hydroxynitrile lyase (EC 4.1.2.46, (R)-HNL, (R)-oxynitrilase, (R)-hydroxynitrile lyase, LuHNL) is an enzyme with systematic name (2R)-2-hydroxy-2-methylbutanenitrile butan-2-one-lyase (cyanide forming). This enzyme catalyses the following chemical reaction:(2R)-2-hydroxy-2-methylbutanenitrile cyanide + butan-2-one