Reaction scheme for the generation of nitric oxide from HU. Based on the reactions proposed by Huang et al²¹  for the oxidation of HU by horseradish peroxidase. Other reactions are also believed to occur (not shown), including the possible direct release of ·NO from the nitroxide radical intermediate, and the dimerization of nitroxyl (HNO) to generate nitrous oxide (N₂O). Illustration by Paulette Dennis.