Figure 1.

Overview of H₂S biogenesis in the mammalian colon. Gut microbiota generate H₂S by fermentation of dietary sulfur-organic compounds and by sulfate reduction (as well as butyrate by fermentation of dietary fiber). H₂S production in colonic epithelial cells occurs through the four enzymes CBS, CTH, MPST and SELENBP1. Sulfur-containing amino acids serve as precursors for H₂S production by CBS, CTH and MPST, while the SELENBP1 substrate methanethiol is produced from methionine by colonic microbiota. SQOR is a key enzyme in H₂S catabolism. Scheme created with Biorender.com.