Figure 9.

Implications of GSH versus sulfite as sulfane sulfur acceptor from SQR on the organization of the mitochondrial sulfide oxidation pathway. A, transfer of two-electron-oxidized sulfide to GSH forms GSSH, which is converted by PDO to sulfite. The latter is a substrate for sulfite oxidase (SO) that resides in the intermitochondrial membrane space and is further oxidized to sulfate. In this scheme rhodanese forms thiosulfate from GSSH and sulfite generated in the mitochondrion. B, transfer of two-electron oxidized sulfide from SQR to six-electron oxidized sulfite generates thiosulfate, which must be transported out of the mitochondrion to undergo a second sulfur transfer reaction catalyzed by TSTD1. The product GSSH, which is highly reactive, must be transported back into the mitochondrion for utilization by PDO. The sulfur atoms derived from H₂S are shown in red. The metabolic logic of pathway B was described as convoluted even by its proponents (11), described under “Discussion,” is considered to be unlikely.