Figure 1.

Scheme showing the intersections between energy metabolism and H₂S oxidation. Reducing equivalents generated in the cytoplasm are moved to the mitochondrion via the malate–aspartate shuttle comprising a neutral α-ketoglutarate–malate and an electrogenic aspartate–glutamate transporter (pink). Conversion of malate to oxaloacetate in the mitochondrion regenerates NADH, which enters the electron transport chain (purple) at the level of complex I (CI). The purple arrows denote proton translocation. The sulfide oxidation pathway (blue) converts H₂S to thiosulfate and sulfate with electrons from the oxidation catalyzed by SQOR entering at the level of complex III (CIII) and from sulfite oxidase (SO) at the level of complex IV (CIV). At higher concentrations, H₂S inhibits CIV. α-KG, MDH1/2, GOT1/2, and IMS denote α-ketoglutarate, malate dehydrogenase 1 and 2, glutamate-oxoglutarate transaminase 1 and 2, and inter mitochondrial membrane space, respectively.