The enzyme casbene synthase (EC 4.2.3.8) catalyzes the chemical reaction
This enzyme belongs to the family of lyases, specifically those carbon-oxygen lyases acting on phosphates. The systematic name of this enzyme class is geranylgeranyl-diphosphate diphosphate-lyase (cyclizing, casbene-forming). Other names in common use include casbene synthetase, and geranylgeranyl-diphosphate diphosphate-lyase (cyclizing). This enzyme participates in diterpenoid biosynthesis.