Figure 2. Overview of the endogenous and exogenous H2S production in the mammalian body. Left panel: The endogenous production of H2S in mammalian cells. Several important enzymes are mentioned along the arrows. Right panel: The exogenous production of H2S in the gastrointestinal tract by the intestinal microbiota and sulfate-reducing bacteria, for which the H2S production is endogenous. The dashed lines between the left and the right panel indicate the transport of molecules between the compartments.