A three-component membrane-bound flavoenzyme that catalyzes the formation of hydrogen cyanide, a secondary metabolite, by transfer of electrons to a cyanide-resistant branch of the aerobic respiratory chain. Contributes to suppression of black root rot of tobacco. 2 A + glycine = 2 AH2 + CO2 + hydrogen cyanide Heterotrimer of HcnA, HcnB and HcnC. Transcriptionally up-regulated by Anr in response to Fe(3+) in oxygen-limiting conditions. Stimulated by glycine. Belongs to the FAD-dependent glycerol-3-phosphate dehydrogenase family.