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 (PubMed:16453871). 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 (PubMed:10570200, PubMed:11021918). Post-transcriptionally up-regulated by GacA (PubMed:10570200). Stimulated by glycine.