Hydrogen sulfide: its production, release and functions

Hydrogen sulfide (H2S), which is a well-known toxic gas, has been recognized as a signal molecule as well as a cytoprotectant. It is produced by three enzymes, cystathionine β-synthase, cystathionine γ-lyase and 3-mercaptopyruvate sulfurtransferase along with cysteine aminotransferase. In addition to an immediate release of H2S from producing enzymes, it can be stored as bound sulfane sulfur, which may release H2S in response to physiological stimuli. As a signal molecule, it modulates neuronal transmission, relaxes smooth muscle, regulates release of insulin and is involved in inflammation. Because of its reputation as a toxic gas, the function as a cytoprotectant has been overlooked: the nervous system and cardiovascular system are protected from oxidative stress. In this review, enzymatic production, release mechanism and functions of H2S are focused on.